Arithmetic decoding device, image decoding apparatus, arithmetic coding device, and image coding apparatus

ABSTRACT

There is provided a terminal device capable of efficiently performing communication in a communication system in which a base station device and the terminal device communicate with each other. The terminal device that communicates with the base station device by using a plurality of aggregated cells recognizes that a serving cell is stopped in a first state, recognizes that the serving cell is started in a second state, and switches from the first state to the second state based on a received PDCCH.

This application is a continuation of U.S. patent application Ser. No.15/635,238 filed Jun. 28, 2017 (pending, which is a continuation of U.S.patent application Ser. No. 15/468,142 filed Mar. 24, 2017 (granted asU.S. Pat. No. 9,794,572), which is a continuation of U.S. patentapplication Ser. No. 15/341,019 filed Nov. 2, 2016 (granted as U.S. Pat.No. 9,699,479), which is a continuation of U.S. patent application Ser.No. 14/402,114 filed Nov. 19, 2014 (granted as U.S. Pat. No. 9,538,205),which is the national stage of PCT application PCT/JP2013/064447 filedMay 24, 2013, which claims priority of JP Application 2012-126567 filedJun. 1, 2012 and JP Application 2012-178842 filed Aug. 10, 2012, theentire content of each of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an arithmetic decoding device whichdecodes coded data that is arithmetically coded, and an image decodingapparatus including the arithmetic decoding device. In addition, thepresent invention relates to an arithmetic coding device which generatescoded data that is arithmetically coded, and an image coding apparatusincluding the arithmetic coding device.

BACKGROUND ART

In order to efficiently transmit or record moving images, a moving imagecoding apparatus (image coding apparatus) which generates coded data bycoding a moving image, and a moving image decoding apparatus (imagedecoding apparatus) which generates a decoded image by decoding thecoded data, are used.

As a specific moving image coding method, for example, there are methods(NPL 1) proposed in H. 264/MPEG-4. AVC, and High-Efficiency Video Coding(HEVC) which is a succeeding codec thereof.

In such moving image coding methods, an image (picture) forming a movingimage is managed in a layer structure which is constituted by a sliceobtained by dividing the image, a coding unit obtained by dividing theslice, and a block and a partition obtained by dividing the coding unit,and the image is commonly coded and decoded for each block.

In addition, in these coding methods, typically, a predicted image isgenerated on the basis of a local coded image obtained by coding anddecoding an input image, and coding is performed on a transformcoefficient which is obtained by performing frequency transform such asdiscrete cosine transform (DCT) on a difference image (also referred toas a “residual image” or “prediction residual” in some cases) betweenthe predicted image and the input image for each block.

As a specific method of coding a transform coefficient, context-basedadaptive variable length coding (CAVLC) and context-based adaptivebinary arithmetic coding (CABAC) are known.

In CAVLC, a one-dimensional vector is generated by sequentially scanningeach transform coefficient, and syntax indicating a value of eachtransform coefficient, syntax indicating a length (also referred to as arun) of consecutive 0s, and the like are coded.

In CABAC, a binarization process is performed on various syntax elementsindicating a transform coefficient, and binary data obtained through thebinarization process is arithmetically coded. Here, the various syntaxelements include a flag indicating whether or not a transformcoefficient is 0, that is, a flag significant_coeff_flag (also referredto as transform coefficient presence/absence flag) indicating whether ornot non-zero transform coefficient is present, syntax elementslast_significant_coeff_x and last_significant_coeff_y indicating aposition of the last non-zero transform coefficient in a process order,and the like.

In addition, in CABAC, when a single symbol (also referred to as 1 bitof binary data, or a Bin) is coded, a context index assigned to aprocess target frequency component is referred to, and arithmetic codingis performed corresponding to probability of occurrence indicated by aprobability state index included in a context variable designated by thecontext index. In addition, the probability of occurrence designated bythe probability state index is updated whenever a single symbol iscoded.

In addition, in NPL 1, two-layer coding is employed as a method ofcoding a non-zero transform coefficient. In the two-layer coding, thetransform unit is split into a plurality of sub-blocks, a flag(significant_coeff_flag) indicating whether or not a transformcoefficient is non-zero is coded for each transform coefficient includedin each sub-block, and a flag (also referred to assignificant_coeff_group_flag, or coded_sub_block_flag) indicatingwhether or not a non-zero transform coefficient is included in eachsub-block is coded in the sub-block units.

Further, in NPL 1, the following coding is performed in accordance witha size of the transform unit (TU). In other words, in the small TU (4×4or 8×8), 4×4 or 8×2 is used as a sub-block size, and a context which isassigned to a frequency component is derived on the basis of a position.In the context derivation based on a position, a context index (alsoreferred to as a position context) which is defined in accordance with aposition of a frequency component in a frequency domain is assigned tothe frequency component.

In addition, in the large TU (16×16, 32×32, 16×4, 4×16, 32×8, or 8×32),4×4 is used as a sub-block size, and a context which is assigned to afrequency component on the basis of periphery reference is derived. Inthe context derivation based on periphery reference, a context index(also referred to as a periphery reference context) which is defined inaccordance with the number of non-zero transform coefficients (that is,significant_coeff_flag is referred to) in peripheral frequencycomponents of a corresponding frequency component is assigned to thefrequency component.

In contrast, NPL 2 submits a proposal to abolish the context derivationbased on periphery reference as described above, and this proposal isexpected to be accepted in the next version (HM7) of an HEVC test model.

NPL 2 proposes that a derivation pattern is selected in accordance withwhether or not a non-zero transform coefficient is present in anadjacent sub-block, and a context index is derived from a position in asub-block according to the selected derivation pattern.

With reference to FIGS. 50 to 52, the proposed content in NPL 2 will bedescribed below. In relation to a process target sub-block X illustratedin FIG. 50, the following patterns are obtained from a state of anon-zero transform coefficient in a sub-block A adjacent to the rightside of the sub-block X and a sub-block B adjacent to the lower sidethereof.

(Pattern 0) A case where a value of a sub-block coefficientpresence/absence flag is 0 in both the right adjacent sub-block(xCG+1,yCG) and the lower adjacent sub-block (xCG,yCG+1)

(Pattern 1) A case where a value of the sub-block coefficientpresence/absence flag is 1 in the right adjacent sub-block (xCG+1,yCG),a value of the sub-block coefficient presence/absence flag is 0 in thelower adjacent sub-block (xCG,yCG+1)

(Pattern 2) A case where a value of the sub-block coefficientpresence/absence flag is 0 in the right adjacent sub-block (xCG+1,yCG),a value of the sub-block coefficient presence/absence flag is 1 in thelower adjacent sub-block (xCG,yCG+1)

(Pattern 3) A case where a value of the sub-block coefficientpresence/absence flag is 1 in both the right adjacent sub-block(xCG+1,yCG) and the lower adjacent sub-block (xCG,yCG+1)

According to NPL 2, a pattern index idxCG indicating the patterns isobtained by using the following Equation (X).

idxCG=significant_coeff_group_flag[xCG+1][yCG]+(significant_coeff_group_flag[xCG][yCG+1]<<1)  (X)

In addition, a context index is derived by using coordinates (xB,yB) inthe sub-block X in a method illustrated in FIG. 51 in accordance withthe pattern index idxCG. With reference to FIG. 51, description will bemade of a value of a context index which is derived in each case of thepatterns 0 to 3.

(Case of Pattern 0)

In a case of the pattern 0, a context index is derived bysigCtx=(xB+yB<=2) ? 1:0.

Values of the context index are arranged as illustrated in FIG. 52 (a).

(Case of Pattern 1)

In a case of the pattern 1, a context index is derived by sigCtx=(yB<=1)? 1:0.

Therefore, as illustrated in FIG. 52(b), values of the context indexesare 1 in the first and second rows of the sub-block, and values of thecontext indexes are 0 in the third and fourth rows of the sub-block.

(Case of Pattern 2)

In a case of the pattern 2, a context index is derived by sigCtx=(xB<=1)? 1:0.

Therefore, as illustrated in FIG. 52(c), values of the context indexesare 1 in the first and second columns of the sub-block, and values ofthe context indexes are 0 in the third and fourth columns of thesub-block.

(Case of Pattern 3)

In a case of the pattern 3, a context index is derived bysigCtx=(xB+yB<=4) ? 2:1.

Therefore, in a case of the pattern 3, if a sum of the coordinate xB inthe horizontal direction and the coordinate yB in the vertical directionof the coordinates (xB,yB) in the sub-block is 4 or less, a value of thecontext index is 1, and, otherwise, a value of the context index is 0.

Therefore, values of the context indexes are arranged as illustrated inFIG. 52(d).

In addition, NPL 3 proposes that, in an 8×8 TU, shapes of sub-blockswhich are different from each other in each scan direction are unifiedto a 4×4 sub-block, and also in 8×8 TU to 32×32 TU, a derivation patternis selected in accordance with whether or not a non-zero transformcoefficient is present in an adjacent sub-block, and a context indexregarding a transform coefficient presence/absence flag is derived froma position in the sub-block according to the selected derivationpattern. Further, according to NPL 3, a proposal is submitted that, inrelation to an 8×8 TU of luminance, contexts regarding a transformcoefficient presence/absence flag are differentiated from each otheraccording to scan directions which are an up-right diagonal directionand a horizontal or vertical direction. In other words, a context isshared in a vertical scan and horizontal scan separately from a contextin an up-right diagonal scan.

CITATION LIST Non Patent Literature

-   NPL 1: “Suggested bug-fixes for HEVC text specification draft 6    (JCTVC-I0030)”, Joint Collaborative Team on Video Coding (JCT-VC) of    ITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG11 9th Meeting: Geneva, CH,    27 Apr. to 7 May 2012 (published in April, 2012)-   NPL 2: “Non-CE3: Simplified context derivation for significance map    (JCTVC-I0296)”, Joint Collaborative Team on Video Coding (JCT-VC) of    ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11 9th Meeting: Geneva,    CH, 27 Apr. to 7 May 2012 (published in April, 2012)-   NPL 3: “Removal of the 8×2/2×8 coefficient groups (JCTVC-J0256)”,    Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG 16 WP    3 and ISO/IEC JTC 1/SC 29/WG 11 10th Meeting: Stockholm, SW, 11 to    20 Jul. 2012 (published in July, 2012)

SUMMARY OF INVENTION Technical Problem

However, in the above-described related art, there remains a problem inthat processes related to coding and decoding of a transform coefficientare complex, and coding efficiency is not sufficient.

The present invention has been made in light of the problems, and anobject thereof is to realize an arithmetic decoding device, an imagedecoding apparatus, an arithmetic coding device, and an image codingapparatus, in which hardware is simplified by simplifying processesrelated to coding and decoding of a transform coefficient, and codingefficiency is improved.

Solution to Problem

In order to solve the above-described problems, an arithmetic decodingdevice according to an embodiment of the present invention decodes codeddata of a transform coefficient obtained by performing frequencytransform on a target image for each unit domain, the device includingsub-block coefficient presence/absence flag decoding means for decodinga sub-block coefficient presence/absence flag indicating whether or notat least one non-zero transform coefficient is included in each of aplurality of sub-blocks into which the unit domain is split; and contextindex deriving means for deriving a context index corresponding to atransform coefficient presence/absence flag indicating whether or notthe transform coefficient of a process target is 0, in which, in a casewhere the non-zero transform coefficient is not included in at least twoadjacent sub-blocks which are adjacent to a process target sub-block,the context index deriving means derives three context indexes havingdifferent values.

In order to solve the above-described problems, an arithmetic decodingdevice according to an embodiment of the present invention decodes codeddata of a transform coefficient obtained by performing frequencytransform on a target image for each unit domain, the device includingsub-block coefficient presence/absence flag decoding means for decodinga sub-block coefficient presence/absence flag indicating whether or notat least one non-zero transform coefficient is included in each of aplurality of sub-blocks into which the unit domain is split; and contextindex deriving means for deriving a context index corresponding to atransform coefficient presence/absence flag indicating whether or notthe transform coefficient of a process target is 0, in which the numberof derived context indexes is different depending on whether or not thenon-zero transform coefficient is included in at least two adjacentsub-blocks which are adjacent to a process target sub-block.

In order to solve the above-described problems, an image decodingapparatus according to an embodiment of the present invention includesthe arithmetic decoding device; inverse frequency transform means forgenerating a residual image by performing inverse frequency transform ona transform coefficient which is decoded by the arithmetic decodingdevice; and decoded image generating means for generating a decodedimage by adding up the residual image generated by the inverse frequencytransform means and a predicted image which is predicted from agenerated decoded image.

In order to solve the above-described problems, an arithmetic codingdevice according to an embodiment of the present inventionarithmetically codes each element of syntax indicating a transformcoefficient obtained by performing frequency transform on a target imagefor each unit domain, the device including sub-block coefficientpresence/absence flag coding means for coding a sub-block coefficientpresence/absence flag indicating whether or not at least one non-zerotransform coefficient is included in each of a plurality of sub-blocksinto which the unit domain is split; and context index deriving meansfor deriving a context index corresponding to a transform coefficientpresence/absence flag indicating whether or not the process targettransform coefficient is 0, in which, in a case where the non-zerotransform coefficient is not included in at least two adjacentsub-blocks which are adjacent to a process target sub-block, the contextindex deriving means derives three context indexes having differentvalues.

In order to solve the above-described problems, an arithmetic codingdevice according to an embodiment of the present inventionarithmetically codes each element of syntax indicating a transformcoefficient obtained by performing frequency transform on a target imagefor each unit domain, the device including sub-block coefficientpresence/absence flag decoding means for coding a sub-block coefficientpresence/absence flag indicating whether or not at least one non-zerotransform coefficient is included in each of a plurality of sub-blocksinto which the unit domain is split; and context index deriving meansfor deriving a context index corresponding to a transform coefficientpresence/absence flag indicating whether or not the process targettransform coefficient is 0, in which the number of derived contextindexes is different depending on whether or not the non-zero transformcoefficient is included in at least two adjacent sub-blocks which areadjacent to a process target sub-block.

In order to solve the above-described problems, an image codingapparatus according to an embodiment of the present invention includestransform coefficient generating means for generating a transformcoefficient by performing frequency transform on a residual imagebetween a coding target image and a predicted image for each unitdomain; and any one of the arithmetic coding devices, in which thearithmetic coding device generates coded data by arithmetically codingsyntax which is a transform coefficient generated by the transformcoefficient generating means.

Advantageous Effects of Invention

As described above, in the arithmetic decoding device according to thepresent invention, when a non-zero transform coefficient is not presentin any of sub-blocks adjacent to the process target sub-block, on thebasis of the determination result, the context index deriving meansderives the context indexes which respectively correspond to a casewhere an occurrence probability of a non-zero transform coefficient islow, a case where an occurrence probability of a non-zero transformcoefficient is high, and a case where an occurrence probability of anon-zero transform coefficient is intermediate between the high case andthe low case, according to a position of a process target transformcoefficient in the process target sub-block.

Therefore, it is possible to realize a context derivation pattern whichis more suitable for an actual occurrence probability of a transformcoefficient, and thus it is possible to improve coding efficiency.

As mentioned above, in the arithmetic decoding device according to thepresent invention, if coordinates of the sub-block having the 4×4 sizeare set to (xB,yB) (where xB is a coordinate in a horizontal direction,yB is a coordinate in a vertical direction, and the upper left side ofthe sub-block is set to an origin (0,0)), when a scan order applied tothe sub-block is up-right diagonal scan, in a case where a determineddirectivity is a vertical direction, the context index deriving meansderives the context index corresponding to a case where an occurrenceprobability of a transform coefficient is higher than in domains otherthan a domain formed by (0,0) to (0,3), (1,0) to (1,2), and (2,0), andin a case where a determined directivity is a horizontal direction, thecontext index deriving means derives the context index corresponding toa case where an occurrence probability of a transform coefficient ishigher than in domains other than a domain formed by (0,0) to (3,0),(0,1) to (2,1), and (0,2).

Therefore, it is possible to suppress changes in context indexes in asub-block when compared with the related art. Accordingly, as describedabove, in hardware which defines the number of repeated 0s and 1s,mounting of the hardware is simplified.

As mentioned above, the arithmetic decoding device according to thepresent invention include transform coefficient decoding means fordecoding a transform coefficient by using a scan order according to adirectivity which is determined by directivity determining means fordetermining a directivity of a distribution of a transform coefficient.

According to the configuration, it is possible to decode a transformcoefficient by using a scan order according to a directivity of adistribution of a transform coefficient. Accordingly, as describedabove, in hardware which defines the number of repeated 0s and 1s,mounting of the hardware is simplified.

As mentioned above, in the arithmetic decoding device according to thepresent invention, the context index deriving means derives the contextindex by using a sum of a coordinate in a horizontal direction and acoordinate in a vertical direction of a process target transformcoefficient in the process target sub-block according to the numbercounted by coefficient-present-sub-block number counting means forcounting the number of sub-blocks including at least one non-zerotransform coefficient for each sub-block adjacent to a process targetsub-block on the basis of the sub-block coefficient presence/absenceflag.

In the configuration, since a sub-block coefficient presence/absenceflag is not differentiated between a right adjacent sub-block and alower adjacent sub-block, it is possible to achieve and effect ofsimplifying mounting of hardware.

As mentioned above, in the arithmetic decoding device according to thepresent invention, the context index deriving means derives the contextindex by using higher-order bits in 2-bit expression of each ofcoordinates in a horizontal direction and a vertical direction of aprocess target transform coefficient in the process target sub-blockaccording to a determination result from pattern determining means fordetermining a pattern of a value of a sub-block coefficientpresence/absence flag which is decoded for each sub-block adjacent to aprocess target sub-block.

As mentioned above, the arithmetic decoding device according to thepresent invention includes transform coefficient decoding means fordecoding a transform coefficient by using a scan order in a partialdomain with respect to respective partial domains each having a 2×2size, obtained by splitting a sub-block having a 4×4 size into fourdomains.

According to the configuration, since coordinates in a scan order (forexample, coordinates of frequency components adjacent to each other inthe scan order) can be prevented from being considerably changed,transform coefficients which have spatially the same kinds ofcharacteristics as each other can be sequentially decoded. As a result,coding efficiency is improved.

As mentioned above, in the arithmetic decoding device according to thepresent invention, the context index deriving means derives the contextindex by using coordinates in the unit domain of the process target inthe process target sub-block according to a directivity determined bydirectivity determining means for determining a directivity of adistribution of transform coefficients on the basis of a sub-blockcoefficient presence/absence flag in a sub-block adjacent to a processtarget sub-block.

According to the configuration, since a context index corresponding to acase where an occurrence probability of a non-zero transform coefficientis high is used in a case where a probability of the presence of thehorizontal edge or the vertical edge is high, it is possible to improvecoding efficiency.

As mentioned above, in the arithmetic decoding device according to thepresent invention, in a case where at least one non-zero transformcoefficient is included in sub-blocks of a predetermined number or moreas a result of determining whether or not at least one non-zerotransform coefficient is included in each of sub-blocks adjacent to aprocess target sub-block on the basis of the sub-block coefficientpresence/absence flag, the context index deriving means derives thecontext index corresponding to a case where an occurrence probability ofa non-zero transform coefficient is high, equally in the process targetsub-block.

Therefore, in a case where an occurrence probability of a non-zerotransform coefficient is equally high, it is possible to derive thecontext index corresponding to a case where an occurrence probability ofa non-zero transform coefficient is high, equally in the process targetsub-block, and thus it is possible to improve coding efficiency.

As described above, according to the present invention, it is possibleto realize hardware simplification by simplifying processes related tocoding and decoding of a transform coefficient, and to improve codingefficiency when compared with the configuration of the related art.

In addition, the arithmetic coding device having a configurationcorresponding to the configuration can achieve the same effects.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a configuration of a coefficientpresence/absence flag coding unit included in a moving image decodingapparatus according to an embodiment of the present invention.

FIG. 2 illustrates data configuration of coded data which is generatedby a moving image coding apparatus according to the embodiment of thepresent invention and is decoded by the moving image decoding apparatus,in which (a) to (d) FIG. 2 are diagrams respectively illustrating apicture layer, a slice layer, a tree block layer, and a CU layer.

(a) to (h) in FIG. 3 are diagrams illustrating a PU split type pattern,and respectively illustrate partition shapes in cases of 2N×2N, 2N×N,2N×nU, 2N×nD, N×2N, nL×2N, and nR×2D; (i) to (o) in FIG. 3 are diagramsillustrating split methods in which a square node is subdivided intosquare or non-square quadtrees in which (i) in FIG. 3 illustrates splitinto square shapes, (j) in FIG. 3 illustrates split into rectangularshapes which are transversely long, (k) in FIG. 3 illustrates split intorectangular shapes which are longitudinally long, (1) in FIG. 3illustrates that a transversely long node is split into rectangularshapes which are transversely long, (m) in FIG. 3 illustrates that atransversely long node is split into square shapes, (n) in FIG. 3illustrates that a longitudinally long node is split into rectangularshapes which are longitudinally long, and (o) in FIG. 3 illustrates thata longitudinally long node is split into square shapes.

FIG. 4 illustrates a relationship between a block and a sub-block, inwhich (a) in FIG. 4 illustrates an example in which a 4×4 TU is formedby a single sub-block including 4×4 components; (b) in FIG. 4illustrates an example in which an 8×8 TU is formed by four sub-blockseach including 4×4 components; and (c) in FIG. 4 illustrates an examplein which a 16×16 TU is formed by sixteen sub-blocks each including 4×4components.

FIG. 5 illustrates a scan order in a decoding process and a codingprocess according to the embodiment, in which (a) in FIG. 5 illustratesthat a sub-block scan is a forward scan, (b) in FIG. 5 illustrates thata scan in a sub-block is a forward scan, (c) in FIG. 5 illustrates thata sub-block scan is a backward scan, and (d) in FIG. 5 illustrates thata scan in a sub-block is a backward scan.

FIG. 6 illustrates a decoding process of a non-zero transformcoefficient in the embodiment in which (a) in FIG. 6 illustrates a scanorder in a case where a block having a TU size of 8×8 is split intosub-blocks each having a size of 4×4, and respective frequencycomponents are scanned in a forward scan; (b) in FIG. 6 exemplifiestransform coefficients (non-zero transform coefficients) which are not 0in a frequency domain a frequency component having a TU size of 8×8; (c)in FIG. 6 illustrates each value of a sub-block coefficientpresence/absence flag significant_coeff_group_flag which is decoded foreach sub-block in a case where decoding target transform coefficientsare ones illustrated in (b) in FIG. 6; (d) in FIG. 6 illustrates eachvalue of syntax significant_coeff_flag indicating the presence orabsence of a non-zero transform coefficient in a case where decodingtarget transform coefficients are ones illustrated in (b) in FIG. 6; (e)in FIG. 6 illustrates an absolute value of each transform coefficientobtained by decoding syntaxes coeff_abs_level_greater1_flag,coeff_abs_level_greater2_flag, and coeff_abs_level_remaining in a casewhere decoding target transform coefficients are ones illustrated in (b)in FIG. 6; and (f) in FIG. 6 illustrates syntax coeff_sign_flag in acase where decoding target transform coefficients are ones illustratedin (b) in FIG. 6.

FIG. 7 is a block diagram illustrating a configuration of a moving imagedecoding apparatus according to the embodiment.

FIG. 8 is a block diagram illustrating a configuration of a variablelength code decoding unit included in the moving image decodingapparatus according to the embodiment.

FIG. 9 is a diagram illustrating directions of intra-prediction whichcan be used in the moving image decoding apparatus according to theembodiment.

FIG. 10 is a diagram illustrating intra-prediction modes and the namecorrelated with corresponding intra-prediction modes.

FIG. 11 is a block diagram illustrating a configuration of aquantization residual information decoding unit included in the movingimage decoding apparatus according to the embodiment of the presentinvention.

FIG. 12 is a table illustrating an example of a scan index scanIdxdesignated by an intra-prediction mode index IntraPredMode and eachvalue of log 2TrafoSize-2.

FIG. 13 illustrates a scan index, in which FIG. 13(a) illustrates a scantype ScanType designated by each value of the scan index ScanIdx; FIG.13(b) illustrates an example of a scan order in horizontal fast scanwhen a TU size is 4×4; FIG. 13(c) illustrates an example of an scanorder in vertical fast scan when a TU size is 4×4; and FIG. 13 (d)illustrates an example of an scan order in up-right diagonal scan when aTU size is 4×4. In addition, the horizontal fast scan illustrated inFIG. 13(b) is characterized in that coefficients are scanned diagonallyin the horizontal direction for each line in the units of smallsub-blocks in which the sub-block is split into upper and lower halves,and the vertical fast scan illustrated in FIG. 13 (c) is characterizedin that coefficients are scanned diagonally in the vertical directionfor each line in the units of small sub-blocks in which the sub-block issplit into left and right halves.

FIG. 14 illustrates a scan order of a block and a sub-block, in whichFIGS. 14(a) to 14(c) illustrate an example of a scan order in each scantype designated by the scan index scanIdx in a case where a TU size is8×8 and a sub-block size is 4×4. In addition, an arrow in the exampleillustrated in each of FIGS. 14(a) to 14(c) indicates forward scandirection. Further, the horizontal fast scan illustrated in FIG. 14(a)is characterized in that coefficients are scanned diagonally in thehorizontal direction for each line in the units of small sub-blocks inwhich the sub-block is split into upper and lower halves, and thevertical fast scan illustrated in FIG. 14(b) is characterized in thatcoefficients are scanned diagonally in the vertical direction for eachline in the units of small sub-blocks in which the sub-block is splitinto left and right halves.

FIG. 15 illustrates a scan order of a block and a sub-block, in whichFIGS. 15(a) to 15(c) illustrate examples of scan orders in the scantypes designated by the scan index scanIdx in a case where a TU size is8×8 and sub-block sizes are different from each other. In addition, anarrow in the example illustrated in each of FIGS. 15(a) to 15(c)indicates forward scan direction. Further, the horizontal fast scanillustrated in FIG. 15(a) is characterized in that coefficients arescanned diagonally in the horizontal direction for each line in theunits of sub-blocks which are transversely long, and the vertical fastscan illustrated in FIG. 15(b) is characterized in that coefficients arescanned diagonally in the vertical direction for each line in the unitsof sub-blocks which are longitudinally long.

FIG. 16 is a block diagram illustrating a configuration of a sub-blockcoefficient presence/absence flag decoding unit according to theembodiment.

FIG. 17 illustrates a decoding process performed by the sub-blockcoefficient presence/absence flag decoding unit according to theembodiment, in which FIG. 17(a) illustrates a target sub-block (xCG,yCG)and an adjacent sub-block (xCG,yCG+1) which is adjacent to the lowerside of the target sub-block; FIG. 17(b) illustrates the targetsub-block (xCG,yCG) and an adjacent sub-block (xCG+1,yCG) which isadjacent to the right side of the target sub-block; and FIG. 17(c)illustrates the target sub-block (xCG,yCG), the adjacent sub-block(xCG,yCG+1) which is adjacent to the lower side of the target sub-block,and the adjacent sub-block (xCG+1,yCG) which is adjacent to the rightside of the target sub-block.

FIG. 18 illustrates coding and decoding processes of a sub-blockcoefficient presence/absence flag according to the embodiment, in whichFIG. 18(a) illustrates transform coefficients which are present in afrequency domain of a 16×16 TU, and FIG. 18(b) illustrates a sub-blockcoefficient presence/absence flag assigned to each sub-block.

FIG. 19 is a diagram illustrating an example of a pseudo-code forderiving a context index from coordinates of a target frequencycomponent in a sub-block according to a pattern index idxCG.

FIG. 20 illustrates arrangements of values of the context indexes in thecontext index derivation method using the pseudo-code illustrated inFIG. 19.

FIG. 21 is a diagram illustrating a scan order in a sub-block.

FIG. 22 illustrates modification examples in which a scan order in atarget sub-block is changed according to whether or not a non-zerotransform coefficient is present in an adjacent sub-block.

FIG. 23 is a diagram illustrating another example of a pseudo-code forderiving a context index from coordinates of a process target frequencycomponent in a sub-block according to a pattern index idxCG.

FIG. 24 illustrates arrangements of values of the context indexes in thecontext index derivation method using the pseudo-code illustrated inFIG. 23.

FIG. 25 is a diagram illustrating still another example of a pseudo-codefor deriving a context index from coordinates of a process targetfrequency component in a sub-block according to a pattern index idxCG.

FIG. 26 illustrates arrangements of values of the context indexes in thecontext index derivation method using the pseudo-code illustrated inFIG. 25.

FIG. 27 illustrates a scan order in four 2×2 partial domains of asub-block.

FIG. 28 is a diagram illustrating still another example of a pseudo-codefor deriving a context index from coordinates of a process targetfrequency component in a sub-block according to a pattern index idxCG.

FIG. 29 illustrates arrangements of values of the context indexes in thecontext index derivation method using the pseudo-code illustrated inFIG. 28.

FIG. 30 is a diagram illustrating a general configuration of apseudo-code for performing a context index derivation method related toModification Example 5.

FIG. 31 illustrates arrangements of values of the context indexes in thecontext index derivation method when a specific threshold value is setin the pseudo-code illustrated in FIG. 30.

FIG. 32 illustrates arrangements of values of the context indexes in thecontext index derivation method when another threshold value is set inthe pseudo-code illustrated in FIG. 30.

FIG. 33 illustrates arrangements of values of the context indexes in thecontext index derivation method when still another threshold value isset in the pseudo-code illustrated in FIG. 30.

FIG. 34 is a diagram illustrating still another example of a pseudo-codefor deriving a context index from coordinates of a process targetfrequency component in a sub-block according to a pattern index idxCG.

FIG. 35 illustrates arrangements of values of the context indexes in thecontext index derivation method using the pseudo-code illustrated inFIG. 33.

FIG. 36 is a diagram illustrating positions of a right adjacentsub-block A, a lower adjacent sub-block B, and a lower-right adjacentsub-block C with respect to a process target sub-block X.

FIG. 37 is a diagram illustrating still another example of a pseudo-codefor deriving a context index from coordinates of a process targetfrequency component in a sub-block according to a pattern index idxCG.

FIG. 38 illustrates arrangements of values of the context indexes in thecontext index derivation method using the pseudo-code illustrated inFIG. 37.

FIG. 39 is a flowchart illustrating a flow of a transform coefficientdecoding process performed by a transform coefficient decoding unitincluded in the moving image decoding apparatus.

FIG. 40 is a flowchart illustrating details of a process of decoding asub-block coefficient presence/absence flag.

FIG. 41 is a flowchart illustrating details of a process of decodingeach non-zero transform coefficient present flag significant_coeff_flagin a sub-block.

FIG. 42 is a flowchart illustrating an example of a flow of a contextindex derivation process in a coefficient presence/absence flag codingunit.

FIG. 43 is a block diagram illustrating a configuration of a movingimage coding apparatus according to an embodiment.

FIG. 44 is a block diagram illustrating a configuration of a variablelength code coding unit included in the moving image coding apparatusaccording to the embodiment.

FIG. 45 is a block diagram illustrating a configuration of aquantization residual information coding unit included in the movingimage coding apparatus according to the embodiment of the presentinvention.

FIG. 46 is a block diagram illustrating a configuration of a sub-blockcoefficient presence/absence flag coding unit according to theembodiment.

FIG. 47 is a block diagram illustrating a second configuration exampleof the coefficient presence/absence flag coding unit according to theembodiment.

FIG. 48 illustrates configurations of transmission equipment equippedwith the moving image coding apparatus and reception equipment equippedwith the moving image decoding apparatus, in which FIG. 48(a)illustrates the transmission equipment equipped with the moving imagecoding apparatus, and FIG. 48(b) illustrates the reception equipment theequipped with the moving image decoding apparatus.

FIG. 49 illustrates configurations of recording equipment equipped withthe moving image coding apparatus and reproducing equipment equippedwith the moving image decoding apparatus, in which FIG. 49(a)illustrates the recording equipment equipped with the moving imagecoding apparatus, and FIG. 49(b) illustrates the reproducing equipmentthe equipped with the moving image decoding apparatus.

FIG. 50 is a diagram illustrating positions of a right adjacentsub-block A and a lower adjacent sub-block B with respect to a processtarget sub-block X.

FIG. 51 is a diagram illustrating an example of a pseudo-code of therelated art for deriving a context index from coordinates of a processtarget frequency component in a sub-block according to a pattern indexidxCG.

FIG. 52 illustrates arrangements of values of the context indexes in thecontext index derivation method using the pseudo-code illustrated inFIG. 51.

FIG. 53 illustrates arrangements of values of the context indexes in thecontext index derivation method when another threshold value is set inthe pseudo-code illustrated in FIG. 30.

FIG. 54 is a diagram illustrating still another example of a pseudo-codefor deriving a context index from coordinates of a process targetfrequency component in a sub-block according to a pattern index idxCG.

FIG. 55 illustrates arrangements of values of the context indexes in thecontext index derivation method using the pseudo-code illustrated inFIG. 54.

FIG. 56 illustrates an example of another pseudo-code for realizingarrangements of the values of the context indexes illustrated in FIG.29.

FIG. 57 illustrates an example of another pseudo-code for realizingarrangements of the values of the context indexes illustrated in FIG.31.

FIG. 58 illustrates an example of another pseudo-code for realizingarrangements of the values of the context indexes illustrated in FIG.32.

FIG. 59 illustrates an example of another pseudo-code for realizingarrangements of the values of the context indexes illustrated in FIG.33.

FIG. 60 illustrates an example of another pseudo-code for realizingarrangements of the values of the context indexes illustrated in FIG.53.

FIG. 61 illustrates arrangements of values of the context indexes in thecontext index derivation method when still another threshold value isset in the pseudo-code illustrated in FIG. 30 (Modification Example5-6).

FIG. 62 is a diagram illustrating still another example of a pseudo-codefor deriving a context index from coordinates of a process targetfrequency component in a sub-block according to a pattern index idxCGrelated to Modification Example 5-6.

FIG. 63 illustrates arrangements of values of the context indexes in thecontext index derivation method when still another threshold value isset in the pseudo-code illustrated in FIG. 30 (Modification Example5-7).

FIG. 64 is a diagram illustrating still another example of a pseudo-codefor deriving a context index from coordinates of a process targetfrequency component in a sub-block according to a pattern index idxCGrelated to Modification Example 5-7.

FIG. 65 is a flowchart illustrating an operation of deriving a contextindex regarding a transform coefficient presence/absence flag in thecoefficient presence/absence flag decoding unit 124 related toModification Example 8.

FIG. 66 illustrates an example of a context index assigned to eachcoefficient position of a 4×4 TU in a position context deriving unit 124b.

FIG. 67 is a flowchart illustrating a more detailed operation of stepSX103-3 of FIG. 65.

FIG. 68 is a table illustrating assignment of context indexes regardinga transform coefficient presence/absence flag related to ModificationExample 8.

FIG. 69 is a table illustrating assignment of context indexes regardinga transform coefficient presence/absence flag in a comparative technique(NPL 3).

FIG. 70 is a diagram illustrating a pseudo-code for deriving a contextindex from coordinates of a process target frequency component in asub-block according to a pattern index idxCG and a scan direction (scanindex scanIdx) related to Modification Example 8-2.

FIG. 71 illustrates arrangements of values of the context indexes in thecontext index derivation method using the pseudo-code illustrated inFIG. 70.

FIG. 72 illustrates arrangements of values of the context indexes wheneach of weight coefficients and threshold values of horizontal fast scanand vertical fast scan of a pattern 0 is set to another value in thepseudo-code illustrated in FIG. 70.

FIG. 73 is a diagram illustrating another example of a pseudo-code forderiving a context index from coordinates of a process target frequencycomponent in a sub-block component according to a pattern index idxCGand a scan direction (scan index scanIdx) related to ModificationExample 8-2.

FIG. 74 is a flowchart illustrating details of an operation of a contextindex offset adding process in the comparative technique (NPL 3), and isa flowchart illustrating details of an operation corresponding to stepSX103 of FIG. 65.

DESCRIPTION OF EMBODIMENTS

A coding apparatus and a decoding apparatus according to an embodimentof the present invention will be described. In addition, the decodingapparatus according to the embodiment decodes a moving image from codeddata. Therefore, hereinafter, this is referred to as a “moving imagedecoding apparatus”. Further, the coding apparatus according to thepresent embodiment generates coded data by coding a moving image.Therefore, hereinafter, this is referred to as a “moving image codingapparatus”.

However, the scope to which the present invention is applicable is notlimited thereto. In other words, as is clear from the followingdescription, features of the present invention are established even if aplurality of frames are not premised. That is, the present invention isgenerally applicable to a decoding apparatus and a coding apparatusregardless of whether or not a target is a moving image or a stillimage.

[Configuration of Coded Data #1]

With reference to FIG. 2, a configuration example of coded data #1 whichis generated by a moving image coding apparatus 2 and is decoded by amoving image decoding apparatus 1 will be described. The coded data #1exemplarily includes a sequence and a plurality of pictures forming thesequence.

In a sequence layer, sets of data which are referred to by the movingimage decoding apparatus 1 in order to decode a process target sequenceare prescribed. The sequence layer includes a sequence parameter setSPS, a picture parameter set PPS, and a picture PICT.

FIG. 2 illustrates structures of hierarchies which are equal to or lowerthan a picture layer in the coded data #1. FIGS. 2(a) to 2(d) arediagrams respectively illustrating a picture layer which prescribed thepicture PICT, a slice layer which prescribed a slice S, a tree blocklayer which prescribed a tree block TBLK, and a CU layer whichprescribed a coding unit (CU) included in the tree block TBLK.

(Picture Layer)

In the picture layer, sets of data which are referred to by the movingimage decoding apparatus 1 in order to decode a process target picturePICT (hereinafter, also referred to as a target picture) are prescribed.The picture PICT includes a picture header PH and slices S₁ to S_(NS)(where NS indicates a total number of slices included in the picturePICT) as illustrated in FIG. 2(a).

In addition, in the following, in a case where the respective slices S₁to S_(NS) are not required to be differentiated from each other, thesubscripts may be omitted. Further, this is also the same for other datawhich is included in the coded data #1 described below and is given asubscript.

The picture header PH includes a coding parameter group which isreferred to by the moving image decoding apparatus 1 in order todetermine a decoding method of a target picture.

(Slice Layer)

In the slice layer, sets of data which are referred to by the movingimage decoding apparatus 1 in order to decode a process target slice S(hereinafter, also referred to as a target slice) are prescribed. Theslice S includes a slice header SH and tree blocks TBLK₁ to TBLK_(NC)(where NC indicates a total number of tree blocks included in the sliceS) as illustrated in FIG. 2(b).

The slice header SH includes a coding parameter group which is referredto by the moving image decoding apparatus 1 in order to determine adecoding method of a target slice. Slice type designation information(slice_type) for designating a slice type is an example of a codingparameter included in the slice header SH.

Slice types which can be designated by the slice type designationinformation may include (1) an I slice which uses only intra-predictionduring coding, (2) a P slice which uses a uni-prediction orintra-prediction during coding, (3) a B slice which uses uni-prediction,bi-prediction, or intra-prediction, and the like.

In addition, the slice header SH includes a filter parameter FP which isreferred to be a loop filter which is included in the moving imagedecoding apparatus 1. The filter parameter FP includes a filtercoefficient group. The filter coefficient group includes (1) tap numberdesignation information for designating the number of taps of filters,(2) filter coefficients a₀ to a_(NT-1) (where NT indicates a totalnumber of filter coefficients included in the filter coefficient group),and (3) an offset.

(Tree Block Layer)

In the tree block layer, sets of data which are referred to by themoving image decoding apparatus 1 in order to decode a process targettree block TBLK (hereinafter, also referred to as a target tree block)are prescribed.

The tree block TBLK includes a tree block header TBLK and coding unitinformation CU₁ to CU_(NL) (where NL indicates a total number of itemsof coding unit information included in the tree block TBLK). Here,first, a description will be made of a relationship between the treeblock TBLK and the coding unit information CU.

The tree block TBLK is split into units for specifying a block size usedfor each process of intra-prediction or inter-prediction and transform.

The units of the tree block TBLK are obtained through recursive quadtreesubdivision. A tree structure obtained through the recursive quadtreesubdivision is hereinafter referred to as a coding tree.

Hereinafter, a unit corresponding to a leaf which is a terminal node ofthe coding tree is referred to as a coding node. In addition, the codingnode is a basic unit in a coding process, and thus the coding node ishereinafter referred to as a coding unit (CU).

In other words, the coding unit information CU₁ to CU_(NL) isinformation corresponding to each coding node (coding unit) which isobtained by performing recursive quadtree subdivision on the tree blockTBLK.

In addition, a root of the coding tree is correlated with the tree blockTBLK. In other words, the tree block TBLK is correlated with the highestnode of a tree structure obtained through quadtree subdivision,recursively including a plurality of coding nodes.

In addition, a size of each coding node is a half of a size of a codingnode (that is, a unit of a one hierarchy higher node of thecorresponding coding node) vertically and horizontally.

Further, a size taken by each coding node depends on size designationinformation and a maximum hierarchical depth of a coding node, includedin the sequence parameter set SPS of the coded data #1. For example, ina case where a size of the tree block TBLK is 64×64 pixels, and themaximum hierarchical depth is 3, a coding node in a hierarchy which isequal to or lower than the tree block TBLK can take any one of fourtypes of sizes, that is, 64×64 pixels, 32×32 pixels, 16×16 pixels, and8×8 pixels.

(Tree Block Header)

Tree block header TBLKH includes coding parameters which are referred toby the moving image decoding apparatus 1 in order to determine adecoding method of a target tree block. Specifically, as illustrated inFIG. 2(c), tree block split information SP_TBLK for designating a splitpattern of a target tree block into respective CUs, and a quantizationparameter difference Δqp (qp_delta) for designating a size of aquantization step, are included.

The tree block split information SP_TBLK is information indicating acoding tree for splitting a tree block, and, specifically, informationfor designating a shape, size, and a position in a target tree block, ofeach CU included in the target tree block.

In addition, the tree block split information SP_TBLK may not explicitlyinclude a shape or a size of a CU. For example, the tree block splitinformation SP_TBLK may be a set of flags (split_coding_unit_flag)indicating the entire target tree block or a partial domain of a treeblock is split into four parts. In this case, a shape or a size of eachCU can be specified by using a shape or a size of a tree block together.

In addition, the quantization parameter difference Δqp is a differenceqp−qp′ between a quantization parameter qp in a target tree block and aquantization parameter qp′ in a tree block which is coded right beforethe corresponding target tree block.

(CU Layer)

In the CU layer, sets of data which are referred to by the moving imagedecoding apparatus 1 in order to decode a process target CU(hereinafter, also referred to as a target CU) are prescribed.

Here, prior to detailed description of content of data included in thecoding unit information CU, a tree structure of data included in the CUwill be described. A coding node is a node of roots of a prediction tree(PT) and a transform tree (TT). The prediction tree and the transformtree will be described.

In the prediction tree, a coding node is split into one or a pluralityof prediction blocks, and a position and a size of each prediction blockare prescribed. In other words, the prediction block is one domain or aplurality of domains which do not overlap each other, forming the codingnode. In addition, the prediction tree includes one or a plurality ofprediction blocks obtained through the above-described split.

A prediction process is performed for each prediction block.Hereinafter, the prediction block which is the unit of prediction isalso referred to as a prediction unit (PU).

Types of splits in the prediction tree roughly include two types ofintra-prediction and inter-prediction.

In a case of intra-prediction, as a split method, there are 2N×2N (whichis the same size as that of a coding node) and N×N.

In addition, in a case of inter-prediction, as a split method, there are2N×2N (which is the same size as that of a coding node), 2N×N, N×2N,N×N, and the like.

Further, in the transform tree, a coding node is split into one or aplurality of transform blocks, and a position and a size of eachtransform block are prescribed. In other words, the transform block isone domain or a plurality of domains which do not overlap each other,forming the coding node. In addition, the transform tree includes one ora plurality of transform blocks obtained through the above-describedsplitting.

A transform process is performed for each prediction block. Hereinafter,the transform block which is the unit of transform is also referred toas a transform unit (TU). A size of the TU is represented by alogarithmic value log 2TrafoWidth of a width and a logarithmic value log2TrafoHeight of a height of a transform block. A size of the TU is alsorepresented by a value log 2TrafoSize obtained from the followingEquation.

log 2TrafoSize=(log 2TrafoWidth+log 2TrafoHeight)>>1

Hereinafter, a TU having a width W×height H is referred to as W×H TU(for example, 4×4 TU).

(Data Structure of Coding Unit Information)

Next, with reference to FIG. 2(d), detailed description will be made ofcontent of data included in the coding unit information CU. Asillustrated in FIG. 2(d), the coding unit information CU includes,specifically, a skip mode flag SKIP, CU prediction type informationPred_type, PT information PTI, and TT information TTI.

[Skip Flag]

The skip flag SKIP is a flag indicating whether or not a skip mode isapplied to a target CU, and in a case where a value of the skip flagSKIP is 1, that is, the skip mode is applied to a target CU, the PTinformation PTI in the coding unit information CU is omitted. Inaddition, the skip flag SKIP is omitted in an I slice.

[CU Prediction Type Information]

The CU prediction type information Pred_type includes CU predictionmethod information PredMode and PU split type information PartMode. TheCU prediction type information is simply referred to as prediction typeinformation in some cases.

The CU prediction method information PredMode is to designate one ofintra-prediction (intra-CU) and inter-prediction (inter-CU) as apredicted image generation method for each PU included in a target CU.In addition, hereinafter, the types of skip, intra-prediction, andinter-prediction are referred to as CU prediction modes in a target CU.

The PU split type information PartMode is to designate a PU split typewhich is a pattern of split of a target coding unit (CU) into PUs.Hereinafter, as mentioned above, dividing target coding unit (CU) intoPUs is referred to as PU split according to a PU split type.

For example, the PU split type information PartMode may be an indexindicating the type of PU split pattern, and may designate a shape, asize, and a position in a target prediction tree, of each PU included inthe target prediction tree.

In addition, a selectable PU split type is different depending on a CUprediction method and a CU size. Further, a selectable PU split type isdifferent in each case of inter-prediction and intra-prediction.Furthermore, details of the PU division type will be described later.

[Pt Information]

The PT information PTI is information regarding a PT included in atarget CU. In other words, the PT information PTI is a set ofinformation regarding each of one or a plurality of PUs included in aPT. As described above, generation of a predicted image is performed inthe units of PUs, and thus the PT information PTI is referred to whenthe predicted image is generated by the moving image decoding apparatus1. The PT information PTI includes PU information PUI₁ to PUI_(NP)(where NP indicates a total number of PUs included in a target PT)including prediction information in each PU as illustrated in FIG. 2(d).

The prediction information PUI includes an image processing apparatusparameter PP_Intra or an inter-prediction parameter PP_Inter accordingto a prediction method designated by the prediction type informationPred_mode. Hereinafter, a PU to which intra-prediction is applied isreferred to as an intra-PU, and a PU to which inter-prediction isapplied is referred to as an inter-PU.

The inter-prediction parameter PP_Inter includes coding parameters whichare referred to when the moving image decoding apparatus 1 generates aninter-predicted image through inter-prediction.

The inter-prediction parameter PP_Inter may be, for example, a mergeflag (merge_flag), a merge index (merge_idx), an estimated motion vectorindex (mvp_idx), a reference image index (ref_idx), an inter-predictionflag (inter_pred_flag), and a motion vector difference (mvd).

The intra-prediction parameter PP_Inter includes coding parameters whichare referred to when the moving image decoding apparatus 1 generates apredicted image through inter-prediction.

The inter-prediction parameter PP_Inter may be, for example, anestimated prediction mode flag, an estimated prediction mode index, anda remaining prediction mode index.

In addition, the intra-prediction parameter may include a PCM mode flagindicating whether or not a PCM mode is used. In a case where the PCMmode flag is coded, and indicates that a PCM mode is used, each of aprediction process (intra), a transform process, and an entropy codingprocess is omitted.

[TT Information]

The TT information TTI is information regarding a TT included in a CU.In other words, the TT information TTI is a set of information regardingeach of one or a plurality of TUs included in a TT, and is referred towhen the moving image decoding apparatus 1 decodes residual data. Inaddition, hereinafter, a TU is referred to as a block in some cases.

As illustrated in FIG. 2(d), the TT information TTI includes TT splitinformation SP_TU, and TU information TUI₁ to TUI_(NT) (where NTindicates a total number of blocks included in a target CU).

The TT split information SP_TU is, specifically, information fordetermining a shape, a size, and a on in a target CU, of each TUincluded in the target CU. For example, the TT split information SP_TUmay be realized by information (split_transform_flag) indicating whetheror not a target node will be split, and information (trafoDepth)indicating a depth of the split.

In addition, for example, in a case where a size of a CU is 64×64, eachTU which is obtained through splitting can take sizes of 32×32 pixels to4×4 pixels.

The TU information TUI₁ to TUI_(NT) is information regarding each of oneor a plurality of TUs included in a TT. For example, the TU informationTUI includes a quantized prediction residual (also referred to as aquantized residual).

Each quantized prediction residual is coded data which is generated bythe moving image coding apparatus 2 performing the following processes 1to 3 on a process target block.

Process 1: Frequency transform (for example, discrete cosine transform(DCT)) is performed on a prediction residual obtained by subtracting apredicted image from a coding target image.

Process 2: A transform coefficient obtained in the process 1 isquantized.

Process 3: Variable length coding is performed on the transformcoefficient quantized in the process 2.

In addition, the quantization parameter qp indicates a size of aquantization step QP which is used for the moving image coding apparatus2 to quantize the transform coefficient (QP=2^(qp/6)).

(PU Split Type)

The PU split type includes a total of the following eight types ofpatterns assuming that a size of a target CU is 2N×2N. In other words,there are four symmetric splitting including 2N×2N pixels, 2N×N pixels,N×2N pixels, and N×N pixels, and four asymmetric splitting including2N×nU pixels, 2N×nD pixels, nL×2N pixels, and nR×2N pixels. In addition,N indicates 2^(m) (where m is an integer of 1 or more). Hereinafter, adomain which is obtained by splitting a symmetric CU is also referred toas a partition.

FIGS. 3(a) to 3(h) specifically illustrate positions of boundaries of PUslit in a CU, for respective slit types.

FIG. 3(a) illustrates a PU split type of 2N×2N in which a CU is notsplit. In addition, FIGS. 3(b), 3(c) and 3(d) respectively illustrateshapes of partitions in cases where PU split types are 2N×N, 2N×nU, and2N×nD. Further, FIGS. 3(e), 3(f) and 3(g) respectively illustrate shapesof partitions in cases where PU split types are N×2N, nL×2N, and nR×2N.Furthermore, FIG. 3(h) illustrates a shape of a partition in a casewhere a PU split type is N×N.

The PU split types of FIGS. 3(a) and 3(h) are also referred to as squaresplit on the basis of the shape of the partition. In addition, the PUsplit types of FIGS. 3(b) to 3(g) are also referred to as non-squaresplit.

Further, in FIGS. 3(a) to 3(h), a number given to each domain indicatesan identification number of the domain, and a process is performed onthe domains in an order of the identification numbers. In other words,the identification number indicates a scan order of the domain.

[Split Type in Case of Inter-Prediction]

In an inter-PU, seven types are defined except for N×N (FIG. 3(h)) amongthe eight split types. In addition, the six asymmetric splittings arereferred to as asymmetric motion partition (AMP).

Further, a specific value of N is prescribed by a size of a CU to whicha corresponding PU belongs, and specific values of nU, nD, nL, and nRare determined according to a value of N. For example, an inter-CU of128×128 pixels can be split into inter-PUs of 128×128 pixels, 128×64pixels, 64×128 pixels, 64×64 pixels, 128×32 pixels, 128×96 pixels,32×128 pixels, and, and 96×128 pixels.

[Split Type in Case of Intra-Prediction]

The following two split patterns are defined in an intra-PU. Thepatterns are a split pattern 2N×2N in which a target CU is not split,that is, the target CU is treated as a single PU, and a pattern N×N inwhich the target CU is symmetrically split into four PUs.

Therefore, the intra-PU can take the split patterns of FIGS. 3(a) and3(h) in the examples illustrated in FIG. 3.

For example, an intra-CPU of 128×128 pixels can be split into 128×128pixels and 64×64 pixels.

(TU Split Type)

Next, a TU split type will be described with reference to FIGS. 3(i) to3(o). Patterns of TU split is determined by a size of a CU, depth(trafoDepth) of split, and a PU split type of a target PU.

In addition, patterns of TU split include square quadtree subdivisionand non-square quadtree subdivision.

FIGS. 3(i) to (k) illustrate split types in which a square node issubdivided into square or non-square quadtrees. More specifically, FIG.3(i) illustrates a split type in which a square node is subdivided intosquare quadtrees. In addition, FIG. 3(j) illustrates a split type inwhich a square node is subdivided into rectangular quadtrees each ofwhich is transversely long. Further, FIG. 3(k) illustrates a split typein which a square node is subdivided into rectangular quadtrees each ofwhich is longitudinally long.

In addition, FIGS. 3(l) to 3(o) illustrate split types in which anon-square node is subdivided into square or non-square quadtrees. Morespecifically, FIG. 3(l) illustrates a split type in which a rectangularnode which is transversely long is subdivided into rectangular quadtreeseach of which is transversely long. In addition, FIG. 3(m) illustrates asplit type in which a rectangular node which is transversely long issubdivided into square quadtrees. Further, FIG. 3(n) illustrates a splittype in which a rectangular node which is longitudinally long issubdivided into rectangular quadtrees each of which is longitudinallylong. Furthermore, FIG. 3(o) illustrates a split type in which arectangular node which is longitudinally long is subdivided into squarequadtrees.

(Configuration of Quantized Residual Information QD)

The quantized residual information QD may include information such as aposition of the last non-zero transform coefficient, the presence orabsence of a non-zero transform coefficient in a sub-block, the presenceor absence of a non-zero transform coefficient at each position, and alevel and a sign of a transform coefficient.

For example, the quantized residual information QD may include syntaxeslast_significant_coeff_x, last_significant_coeff_y,significant_coeff_group_flag, significant_coeff_flag,coeff_abs_level_greater1_flag, coeff_abs_level_greater2_flag,coeff_sign_flag, and coeff_abs_level_remaining.

Transform coefficients are sequentially scanned from a low frequencyside toward a high frequency side. This scan order may be referred to asa forward scan. On the other hand, reversely to the forward scan, a scanfrom a high frequency side to a low frequency side is also used. Thisscan order may be referred to as a backward scan.

The syntaxes last_significant_coeff_x and last_significant_coeff_y aresyntaxes indicating a position of the last non-zero transformcoefficient in the forward scan direction. In addition, each syntax maybe subdivided into prefix and suffix and be coded. A last coefficientposition may be derived by using last coefficient process prefixeslast_significant_coeff_x_prefix and last_significant_coeff_y_prefix andlast coefficient position suffixes last_significant_coeff_x_suffix, andlast_significant_coeff_y_suffix.

The syntax significant_coeff_flag is a syntax indicating the presence orabsence of a non-zero transform coefficient in each frequency componentin the backward scan direction with a non-zero transform coefficient asa starting point. The syntax significant_coeff_flag is a flag whichtakes 0 if a transform coefficient is 0 and takes 1 if a transformcoefficient is not 0, with respect to each of xC and yC. In addition,the syntax significant_coeff_flag is also referred to as a transformcoefficient presence/absence flag or simply referred to as coefficientpresence/absence flag. Further, significant_coeff_flag may not betreated as a separate syntax but may be included in the syntax (forexample, coeff_abs_level) indicating an absolute value of a transformcoefficient. In this case, a first bit of the syntax coeff_abs_levelcorresponds to significant_coeff_flag, and the following process ofderiving a context index of significant_coeff_flag corresponds to aprocess of deriving a context index of the first bit of the syntaxcoeff_abs_level.

A variable length code decoding unit 11 included in the moving imagedecoding apparatus 1 splits a tree block into a plurality of sub-blocks,and decodes significant_coeff_group_flag in the process units ofsub-blocks. The quantized residual information QD includes a flag(sub-block coefficient presence/absence flagsignificant_coeff_group_flag) indicating that at least one non-zerotransform coefficient in the sub-block in the sub-block units.

Hereinafter, with reference to FIGS. 4 to 6, a summary of a decodingprocess will be described.

First, with reference to FIG. 4, an example of sub-block splitting willbe described. FIG. 4 illustrates a relationship between a block and asub-block. FIG. 4(a) illustrates an example in which a 4×4 TU is formedby a single sub-block including 4×4 components. FIG. 4(b) illustrates anexample in which an 8×8 TU is formed by four sub-blocks each including4×4 components. FIG. 4(c) illustrates an example in which a 16×16 TU isformed by sixteen sub-blocks each including 4×4 components. In addition,a relationship between a TU size and a sub-block size and a splittingmethod are not limited to these examples.

FIG. 5(a) is a diagram illustrating a scan order for a plurality of (inFIG. 5(a), 4×4=16) sub-blocks obtained by splitting a block.Hereinafter, a scan in the units of sub-blocks is also referred to as asub-block scan. In a case where the sub-blocks are scanned as in FIG.5(a), respective frequency domains in the sub-blocks are scanned in ascan order illustrated in FIG. 5(b). The scan order illustrated in FIGS.5(a) and 5(b) is referred to as a “forward scan”.

FIG. 5(c) is a diagram illustrating a scan order for a plurality of (inFIG. 5(b), 4×4=16) sub-blocks obtained by splitting a block. In a casewhere the sub-blocks are scanned as in FIG. 5(c), respective frequencydomains in the sub-blocks are scanned in a scan order illustrated inFIG. 5(d). The scan order illustrated in FIGS. 5(c) and 5(d) is referredto as a “backward scan”.

A transverse axis of each of FIGS. 6(a) to 6(f) expresses a horizontalfrequency xC (where 0≤xC≤7), and a longitudinal axis thereof expresses avertical frequency yC (where 0≤yC≤7). In the following description,among partial domains included in a frequency domain, a partial domaindesignated by the horizontal frequency xC and the vertical frequency yCis also referred to as a frequency component (xC,yC). In addition, atransform coefficient for the frequency component (xC,yC) is alsodenoted by Coeff (xC,yC). A transform coefficient Coeff (0,0) indicatesa DC component, and other transform coefficients indicate componentsother than the DC component. In the present specification, (xC,yC) maybe denoted as (u,v).

FIG. 6(a) is a diagram illustrating a scan order in a case where a blockhaving a TU size of 8×8 is split into sub-blocks each having a size of4×4, and respective frequency components are scanned in the forwardscan.

FIG. 6(b) is a diagram exemplifying non-zero transform coefficients in afrequency domain including 8×8 frequency components. In a case of theexample illustrated in FIG. 6(b), last_significant_coeff_x is 6, andlast_significant_coeff_y is 0.

FIG. 6(c) is a diagram illustrating each value of the sub-blockcoefficient presence/absence flag significant_coeff_group_flag which isdecoded for each sub-block in a case where decoding target transformcoefficients are ones illustrated in FIG. 6(b). A value ofsignificant_coeff_group_flag regarding a sub-block including at leastone non-zero transform coefficient is set to 1, and a value ofsignificant_coeff_group_flag regarding a sub-block including no non-zerotransform coefficient is set to 0.

FIG. 6(d) is a diagram illustrating each value of the syntaxsignificant_coeff_flag indicating the presence or absence of a non-zerotransform coefficient in a case where decoding target transformcoefficients are ones illustrated in FIG. 6(b). For a sub-block in whichsignificant_coeff_group_flag is 1, significant_coeff_flag is decoded inthe backward scan order, and for a sub-block in whichsignificant_coeff_group_flag is 0, significant_coeff_flag for all thefrequency components included in the sub-block is set to 0 withoutdecoding significant_coeff_flag (a lower left sub-block of FIG. 6(d)).

FIG. 6(e) is a diagram illustrating each value obtained by decoding thesyntaxes coeff_abs_level_greater1_flag, coeff_abs_level_greater2_flag,and coeff_abs_level_remaining in a case where decoding target transformcoefficients are ones illustrated in FIG. 6(b).

FIG. 6(f) is a diagram illustrating the syntax coeff_sign_flag in a casewhere decoding target transform coefficients are ones illustrated inFIG. 6(b).

Decoding of the syntaxes coeff_abs_level_greater1_flag,coeff_abs_level_greater2_flag, and coeff_abs_level_remaining indicatinga value of each transform coefficient changes in accordance with a mode(high throughput mode). The high throughput mode is turned off at thetime of start of a sub-block, and the high throughput mode is turned onat the time when the number of non-zero transform coefficients in asub-block is equal to or larger than a predetermined constant. In thehigh throughput mode, decoding of some syntaxes is skipped.

The syntax coeff_abs_level_greater1_flag is a flag indicating whether ornot an absolute value of a transform coefficient exceeds 1, and is codedfor a frequency component in which a value of the syntaxsignificant_coeff_flag is 1. When a value of a transform coefficientexceeds 1, a value of coeff_abs_level_greater1_flag is 1, and,otherwise, a value of coeff_abs_level_greater1_flag is 0. In addition,decoding of coeff_abs_level_greater1_flag is skipped in the highthroughput mode.

The syntax coeff_abs_level_greater2_flag is a flag indicating whether ornot an absolute value of a transform coefficient exceeds 2, and is codedwhen a value of coeff_abs_level_greater1_flag is 1. When an absolutevalue of a transform coefficient exceeds 2, a value ofcoeff_abs_level_greater2_flag is 1, and, otherwise, a value ofcoeff_abs_level_greater2_flag is 0. In addition, decoding ofcoeff_abs_level_greater2_flag is skipped after the first time in eachsub-block, and in a case of the high throughput mode.

In a case where an absolute value of a transform coefficient is apredetermined base level baseLevel, the syntax coeff_abs_level_remainingis syntax for designating an absolute value of the transformcoefficient. In a case where decoding of coeff_abs_level_greater1_flagis skipped, coeff_abs_level_greater2_flag is skipped, and in a casewhere coeff_abs_level_greater1_flag is 1, coeff_abs_level_greater2_flagis coded when a value thereof is 1. A value of the syntaxcoeff_abs_level_remaining is obtained by subtracting baseLevel from anabsolute value of a transform coefficient. For example,coeff_abs_level_remaining=1 indicates that an absolute value of atransform coefficient is baseLevel+1. In addition, baseLevel isdetermined as follows.

baseLevel=1 (in a case where decoding of coeff_abs_level_greater1_flagis skipped)

baseLevel=2 (in a case where decoding of coeff_abs_level_greater2_flagis skipped in cases other than the above-described case)

baseLevel=3 (in a case where decoding of coeff_abs_level_greater2_flagis 1 in cases other than the above-described cases)

The syntax coeff_sign_flag is a flag indicating a sign (positive ornegative) of a transform coefficient, and is coded for a frequencycomponent in which a value of the syntax coeff_sign_flag is 1 except fora case of performing sign hiding. The syntax coeff_sign_flag takes 1 ifa transform coefficient is positive, and takes 0 if a transformcoefficient is negative.

In addition, the sign hiding refers to a method in which a sign of atransform coefficient is not explicitly coded but is calculated throughcomputation.

The variable length code decoding unit 11 included in the moving imagedecoding apparatus 1 can generate a transform coefficient Coeff (xC,yC)for each frequency component by decoding the syntaxeslast_significant_coeff_x, last_significant_coeff_y,significant_coeff_flag, coeff_abs_level_greater1_flag,coeff_abs_level_greater2_flag, and coeff_sign_flag,coeff_abs_level_remaining.

In addition, a set of non-zero transform coefficients in a specificdomain (for example, a TU) is also referred to significancemap in somecases.

Details of decoding processes of various syntaxes will be describedlater, and a configuration of the moving image decoding apparatus 1 willnow be described.

(Moving Image Decoding Apparatus 1)

Hereinafter, a description will be made of the moving image decodingapparatus 1 according to the present embodiment with reference to FIG. 1and FIGS. 7 to 26. The moving image decoding apparatus 1 is a decodingapparatus which employs the technique proposed in High-Efficiency VideoCoding (HEVC) which is a succeeding codec of the H. 264/MPEG-4. AVCstandard.

FIG. 7 is a block diagram illustrating a configuration of the movingimage decoding apparatus 1. As illustrated in FIG. 7, the moving imagedecoding apparatus 1 includes the variable length code decoding unit 11,a predicted image generating unit 12, an inverse quantization/inversetransform unit 13, an adder 14, a frame memory 15, and a loop filter 16.In addition, as illustrated in FIG. 7, the predicted image generatingunit 12 includes a motion vector recovering unit 12 a, aninter-predicted image generating unit 12 b, an intra-predicted imagegenerating unit 12 c, and a prediction type determining unit 12 d. Themoving image decoding apparatus 1 is an apparatus which generates amoving image #2 by decoding the coded data #1.

(Variable Length Code Decoding Unit 11)

FIG. 8 is a block diagram illustrating a main part configuration of thevariable length code decoding unit 11. As illustrated in FIG. 8, thevariable length code decoding unit 11 includes a quantized residualinformation decoding unit 111, a prediction parameter decoding unit 112,a prediction type information decoding unit 113, and a filter parameterdecoding unit 114.

The variable length code decoding unit 11 decodes a prediction parameterPP regarding each partition from the coded data #1 in the predictionparameter decoding unit 112 and supplies the prediction parameter PP tothe predicted image generating unit 12. Specifically, the predictionparameter decoding unit 112 decodes inter-prediction parameters PP_Interincluding a reference image index, an estimation motion vector index,and a motion vector residual from the coded data #1 in relation to aninter-prediction partition, and supplies the inter-prediction parametersPP_Inter to the motion vector recovering unit 12 a. On the other hand,in relation to an intra-prediction partition, intra-predictionparameters PP_Intra including an estimated prediction mode flag, anestimated prediction mode index, and a remaining prediction mode indexare decoded from the coded data #1, and are supplied to theintra-predicted image generating unit 12 c.

In addition, the variable length code decoding unit 11 decodes theprediction type information Pred_type for each partition from the codeddata #1 in the prediction type information decoding unit 113, andsupplies the prediction type information to the prediction typedetermining unit 12 d. Further, the variable length code decoding unit11 decodes the quantized residual information QD regarding a block, andthe quantization parameter difference Δpq from the coded data #1 in thequantized residual information decoding unit 111, and supplies thedecoded information to the inverse quantization/inverse transform unit13. Furthermore, the variable length code decoding unit 11 decodes thefilter parameter PP from the coded data #1 in the filter parameterdecoding unit 114 and supplies the filter parameter to the loop filter16. Moreover, a specific configuration of the quantized residualinformation decoding unit 111 will be described later, and thusdescription thereof is omitted here.

(Predicted Image Generating Unit 12)

The predicted image generating unit 12 identifies whether each partitionis an inter-prediction partition on which inter-prediction is to beperformed or an intra-prediction partition on which intra-prediction isto be performed on the basis of the prediction type informationPred_type for each partition. In addition, in the former case, aninter-predicted image Pred_Inter is generated, and the generatedinter-predicted image Pred_Inter is supplied to the adder 14 as apredicted image Pred, and, in the latter case, an intra-predicted imagePred_Intra is generated, and the generated intra-predicted imagePred_Intra is supplied to the adder 14. Further, in a case where a skipmode is applied to a process target TU, the predicted image generatingunit 12 omits decoding of other parameters which belongs to the PU.

(Motion Vector Recovering Unit 12 a)

The motion vector recovering unit 12 a recovers a motion vector mvregarding each inter-prediction partition from a motion vector residualregarding the partition and a recovered motion vector mv′ regardinganother partition. Specifically, (1) an estimation motion vector isderived from the recovered motion vector mv′ an estimation methoddesignated by the estimation motion vector index, and (2) the motionvector mv is obtained by adding the derived estimation motion vector tothe motion vector residual. In addition, the recovered motion vector mv′regarding another partition may be read from the frame memory 15. Themotion vector recovering unit 12 a supplies the recovered motion vectormv to the inter-predicted image generating unit 12 b along with acorresponding reference image index RI.

(Inter-Predicted Image Generating Unit 12 b)

The inter-predicted image generating unit 12 b generates a motioncompensation image me regarding each inter-prediction partition throughinter-frame prediction. Specifically, the motion compensation image meis generated from an adaptive filtered decoded image P_ALF′ designatedby the reference image index RI which is supplied from the motion vectorrecovering unit 12 a, by using the motion vector mv supplied from themotion vector recovering unit 12 a. Here, the adaptive filtered decodedimage P_ALF′ is an image obtained by the loop filter 16 performing afilter process on a decoded image in which decoding of all frames havealready been completed, and the inter-predicted image generating unit 12b may read a pixel value of each pixel forming the adaptive filtereddecoded image P_ALF′ from the frame memory 15. The motion compensationimage me generated by the inter-predicted image generating unit 12 b issupplied to the prediction type determining unit 12 d as theinter-predicted image Pred_Inter.

(Intra-Predicted Image Generating Unit 12 c)

The intra-predicted image generating unit 12 c generates a predictedimage Pred_Intra regarding each intra-prediction partition.Specifically, first, a prediction mode is specified on the basis of theintra-prediction parameters PP_Intra supplied from the variable lengthcode decoding unit 11, and assigns the specified prediction mode to atarget partition, for example, in a raster scan order.

Here, specification of a prediction mode based on the intra-predictionparameters PP_Intra may be performed as follows. (1) The estimatedprediction mode flag is decoded, and, in a case where the estimatedprediction mode flag indicates that a prediction mode for a processtarget partition is the same as prediction modes assigned to peripheralpartitions of the target partition, the prediction mode which isassigned to the peripheral partitions of the target partition isassigned to the target partition. (2) On the other hand, in a case wherethe estimated prediction mode flag indicates that a prediction mode fora process target partition is not the same as prediction modes assignedto peripheral partitions of the target partition, the remainingprediction mode index is decoded, and a prediction mode indicated by theremaining prediction mode index is assigned to the target partition.

The intra-predicted image generating unit 12 c generates the predictedimage Pred_Intra from a (locally) decoded image P through inter-frameprediction according to a prediction method indicated by the predictionmode assigned to the target partition. The intra-predicted imagePred_Intra generated by the intra-predicted image generating unit 12 cis supplied to the prediction type determining unit 12 d. In addition,the intra-predicted image generating unit 12 c may generate thepredicted image Pred_Intra from the adaptive filtered decoded imageP_ALF through inter-frame prediction.

With reference to FIG. 9, definition of the prediction mode will bedescribed. FIG. 9 illustrates a definition of the prediction mode. Asillustrated in FIG. 9, thirty-six types of prediction modes are defined,and the prediction modes are specified by numbers of “0” to “35”(intra-prediction mode indexes). In addition, as illustrated in FIG. 10,the following name is assigned to each prediction mode. In other words,“0” is “Intra_Planar (planar prediction mode)”, “1” is “Intra DC(intra-DC prediction mode)”, “2” to “34” are “Intra Angular (directionprediction)”, and “35” is “Intra From Luma”. “35” is specific to achroma prediction mode, and is a mode for performing chroma predictionon the basis of prediction of luminance. In other words, the chromaprediction mode “35” is a prediction mode using a luminance pixel valueand a chroma pixel value. The chroma prediction mode “35” is alsoreferred to as an LM mode. The number of prediction modes(intraPredModeNum) is “35” regardless of a size of a target block.

(Prediction Type Determining Unit 12 d)

The prediction type determining unit 12 d determines whether eachpartition is an inter-prediction partition on which inter-prediction isto be performed or an intra-prediction partition on whichintra-prediction is to be performed on the basis of the prediction typeinformation Pred_type for a PU to which each partition belongs. Inaddition, in the former case, the inter-predicted image Pred_Intergenerated in the inter-predicted image generating unit 12 b is suppliedto the adder 14 as a predicted image Pred, and, in the latter case, theintra-predicted image Pred_Intra is generated in the intra-predictedimage generating unit 12 c is supplied to the adder 14 as a predictedimage Pred.

(Inverse Quantization/Inverse Transform Unit 13)

The inverse quantization/inverse transform unit 13 (1) inverselyquantizes the transform coefficient Coeff which has been decoded fromthe quantized residual information QD of the coded data #1, (2) performsinverse frequency transform such as inverse discrete cosine transform(DCT) on a transform coefficient Coeff_IQ obtained through the inversequantization, and (3) supplies a prediction residual D obtained throughthe inverse frequency transform to the adder 14. In addition, in a casewhere the transform coefficient Coeff decoded from the quantizedresidual information QD is inversely quantized, the inversequantization/inverse transform unit 13 derives a quantization step QPfrom the quantization parameter difference Δqp supplied from thevariable length code decoding unit 11. The quantization parameter qp maybe derived by adding the quantization parameter difference Δpq to aquantization parameter qp′ regarding a TU which is previously subject toinverse quantization and inverse frequency transform, and thequantization step QP may be derived from the quantization parameter qpby, for example, QP=2^(pq/6). In addition, the generation of theprediction residual D by the inverse quantization/inverse transform unit13 is performed in the unit of TU or in the units of blocks into whichthe TU is split.

In addition, for example, if a size of a target block is 8×8, a positionof a pixel in the target block is set to (i,j) (where 0≤i≤7 and 0≤i≤7),a value of the prediction residual D at the position (i,j) is indicatedby D(i,j), and a transform coefficient which is inversely quantized in afrequency component (u,v) (where 0≤u≤7 and 0≤v≤7) is indicated byCoeff_IQ(u,v), the inverse DCT performed by the inversequantization/inverse transform unit 13 is given by, for example, thefollowing Equation (1).

$\begin{matrix}{\mspace{79mu} \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack} & \; \\{{D\left( {i,j} \right)} = {\frac{1}{4}{\sum\limits_{u = 0}^{7}{\sum\limits_{v = 0}^{7}{{C(u)}{C(v)}{Coeff\_ IQ}\left( {u,v} \right)\cos \left\{ \frac{\left( {{2i} + 1} \right)u\; \pi}{16} \right\} \cos \left\{ \frac{\left( {{2j} + 1} \right)v\; \pi}{16} \right\}}}}}} & (1)\end{matrix}$

Here, (u,v) are variables corresponding to the above-described (xC,yC).C(u) and C(v) are given as follows.

C(u)=1/√2 (u=0)

C(u)=1 (u≠0)

C(v)=1/√2 (v=0)

C(v)=1 (v≠0)

(Adder 14)

The adder 14 generates a decoded image P by adding the predicted imagePred supplied from the predicted image generating unit 12 to theprediction residual D supplied from the inverse quantization/inversetransform unit 13. The generated decoded image P is stored in the framememory 15.

(Loop Filter 16)

The loop filter 16 functions (1) as a deblocking filter (DF) whichperforms smoothing (deblock process) on a peripheral image on a blockboundary or a partition boundary in the decoded image P, and (2) as anadaptive filter (ALF) of performing an adaptive filter process on theimage to which the deblocking filter has been applied, by using thefilter parameter FP.

(Details of Quantized Residual Information Decoding Unit 111)

The quantized residual information decoding unit 111 has a configurationfor decoding the quantized transform coefficient Coeff (xC,yC) for eachfrequency component (xC,yC) from the quantized residual information QDincluded in the coded data #1. Here, xC and yC are indexes indicating aposition of each frequency component in a frequency domain, and areindexes which respectively correspond to the horizontal frequency u andthe vertical frequency v described above. Hereinafter, the quantizedtransform coefficient Coeff may be also simply referred to as atransform coefficient Coeff.

FIG. 11 is a block diagram illustrating a configuration of the quantizedresidual information decoding unit 111. As illustrated in FIG. 11, thequantized residual information decoding unit 111 includes a transformcoefficient decoding unit 120 and an arithmetic code decoding unit 130.

(Arithmetic Code Decoding Unit 130)

The arithmetic code decoding unit 130 has a configuration for decodingeach bit included in the quantized residual information QD by referringto context, and includes a context recording/updating unit 131 and a bitdecoding unit 132 as illustrated in FIG. 11.

[Context Recording/Updating Unit 131]

The context recording/updating unit 131 has a configuration forrecording and updating a context variable CV which is managed by eachcontext index ctxIdx. Here, the context variable CV includes (1) asuperior symbol MPS (most probable symbol) of which an occurrenceprobability is high, and (2) a probability state index pStateIdx fordesignating an occurrence probability of the superior symbol MPS.

The context recording/updating unit 131 updates the context variable CVby referring to the context index ctxIdx supplied from each constituentelement included in the transform coefficient decoding unit 120 and avalue of a Bin decoded by the bit decoding unit 132, and records theupdated context variable CV until the next update. In addition, thesuperior symbol MPS is 0 or 1. Further, the superior symbol MPS and theprobability state index pStateIdx are updated whenever the bit decodingunit 132 decodes a single Bin.

In addition, the context index ctxIdx may directly designate context foreach frequency component, and may be an increment value from an offsetof a context index which is set for each TU which is a process target(this is also the same for the following).

[Bit Decoding Unit 132]

The bit decoding unit 132 decodes each bit (also referred to as a Bin)included in the quantized residual information QD by referring to thecontext variable CV which is recorded in the context recording/updatingunit 131. In addition, a value of the Bin obtained through the decodingis supplied to each constituent element included in the transformcoefficient decoding unit 120. Further, a value of the Bin obtainedthrough the decoding is also supplied to the context recording/updatingunit 131 so as to be referred to for updating the context variable CV.

(Transform Coefficient Decoding Unit 120)

As illustrated in FIG. 11, the transform coefficient decoding unit 120includes a last coefficient position decoding unit 121, a scan ordertable storage unit 122, a coefficient decoding control unit 123, acoefficient presence/absence flag decoding unit, a coefficient valuedecoding unit 125, a decoded coefficient storage unit 126, and asub-block coefficient presence/absence flag decoding unit 127.

[Last Coefficient Position Decoding Unit 121]

The last coefficient position decoding unit 121 analyzes the decoded bit(Bin) supplied from the bit decoding unit 132 so as to decodelast_significant_coeff_x and last_significant_coeff_y. The decodedsyntaxes last_significant_coeff_x and last_significant_coeff_y aresupplied to the coefficient decoding control unit 123. In addition, thelast coefficient position decoding unit 121 calculates the context indexctxIdx for determining context used to decode Bin of the syntaxeslast_significant_coeff_x and last_significant_coeff_y in the arithmeticcode decoding unit 130. The calculated context index ctxIdx is suppliedto the context recording/updating unit 131.

[Scan Order Table Storage Unit 122]

The scan order table storage unit 122 stores a table which provides aposition of a process target frequency component in a frequency domainby using a size of a process target TU (block), a scan index indicatingthe type of scan direction, and a frequency component identificationindex which is given according to a scan order, as arguments.

An example of such a scan order table may include ScanOrder. ScanOrderis a table for obtaining a position (xC,yC) in a frequency domain of aprocess target frequency component on the basis of a width size log2TrafoWidth of a process target TU, a height size log 2TrafoHeight ofthe process target TU, a scan index scanIdx, and a frequency componentidentification index n which is given according to a scan order. Inaddition, hereinafter, a position (xC,yC) in a frequency domain of aprocess target frequency component may be simply referred to as acoefficient position (xC, yC).

Further, the table stored in the scan order table storage unit 122 isdesignated by a size of a process target TU (block) and the scan indexscanIdx associated with a prediction mode index of an intra-predictionmode. In a case where a prediction mode method used for a process targetTU is intra-prediction, the coefficient decoding control unit 123 refersto a table which is designated by a size of the TU and the scan indexscanIdx associated with a prediction mode of the TU, so as to determinea scan order of frequency components.

FIG. 12 illustrates an example of the scan index scanIdx which isdesignated by an intra-prediction mode index IntraPredMode and a valuelog 2TrafoSize for designating a TU size. In FIG. 12, log 2TrafoSize-2=0indicates that a TU size is 4×4 (corresponding to 4×4 pixels), and log2TrafoSize-2=1 indicates that a TU size is 8×8 (corresponding to 8×8pixels). In addition, log 2TrafoSize-2=2 and log 2TrafoSize-2=3respectively indicate TU sizes of 16×16 and 32×32.

As illustrated in FIG. 12, for example, in a case where the TU size is4×4, and the intra-prediction mode index is 1, the scan index of 0 isused, and, in a case where the TU size is 4×4, and the intra-predictionmode index is 6, the scan index of 2 is used.

FIG. 13(a) illustrates a scan type ScanType designated by each value ofthe scan index scanIdx. As illustrated in FIG. 13(a), in a case wherethe scan index is 0, an up-right diagonal scan is designated; in a casewhere the scan index is 1, a horizontal fast scan is designated; and ina case where the scan index is 2, a vertical fast scan is designated.

In addition, in a case where the CU prediction method informationPredMode is inter-prediction, a scan index may be derived by using a TUsize. In a case where, in a TU size, a width and a height of the TU sizeare the same as each other, a scan order (scan index=0) other than thehorizontal fast scan and vertical fast scan is used. In a case where awidth and a height of the TU size are not the same as each other, and awidth of the TU size is larger than the height thereof, the horizontalfast scan order (scan index=1) is used. On the other hand, in a casewhere a height of a TU size is larger than a width thereof, the verticalfast scan order (scan index=2) is used.

In addition, FIGS. 13(b) to 13(d) illustrate examples of scan orders ofthe respective scan types (the horizontal fast scan, the vertical fastscan, and the up-right diagonal scan) designated by the scan indexscanIdx in a case where a TU size is 4×4. Further, the respectiveexamples illustrated in FIGS. 13(b) to 13(d) illustrate a forward scandirection. The horizontal fast scan illustrated in FIG. 13(b) ischaracterized in that coefficients are scanned diagonally in thehorizontal direction for each line in the units of small sub-blocks inwhich the sub-block is split into upper and lower halves, and issuitable for a case where coefficients concentrate on horizontalfrequency components. In addition, the vertical fast scan illustrated inFIG. 13(c) is characterized in that coefficients are scanned diagonallyin the vertical direction for each line in the units of small sub-blocksin which the sub-block is split into left and right halves, and issuitable for a case where coefficients concentrate on vertical frequencycomponents.

FIGS. 14(a) to 14(c) illustrate an example of a scan order in each scantype designated by the scan index scanIdx in a case where a TU size is8×8 and a sub-block size is 4×4. In addition, each example illustratedin FIGS. 14(a) to 14(c) illustrates a forward scan direction. Thehorizontal fast scan illustrated in FIG. 14(a) is characterized in thatcoefficients are scanned diagonally in the horizontal direction for eachline in the units of small sub-blocks in which the sub-block is splitinto upper and lower halves, and is suitable for a case wherecoefficients concentrate on horizontal frequency components. Inaddition, the vertical fast scan illustrated in FIG. 14(b) ischaracterized in that coefficients are scanned diagonally in thevertical direction for each line in the units of small sub-blocks inwhich the sub-block is split into left and right halves, and is suitablefor a case where coefficients concentrate on vertical frequencycomponents. Further, the up-right diagonal scan illustrated in FIG.14(c) is characterized in that coefficients are scanned in an upperright diagonal direction, and is suitable for a case where there is noparticular directivity in a distribution of coefficients.

FIG. 15 illustrates examples of scan orders in the scan types designatedby the scan index scanIdx in a case where a TU size is 8×8 and sub-blocksizes are different from each other.

FIG. 15(a) illustrates an example of the horizontal fast scan in a casewhere a TU size is 8×8, and a sub-block size is 8×2. The method in whichcoefficients are scanned diagonally in the horizontal direction for eachline in the units of 8×2 sub-blocks (transversely long sub-blocks)illustrated in FIG. 15(a) is suitable for a case where coefficientsconcentrate on horizontal frequency components.

FIG. 15(b) illustrates an example of the vertical fast scan in a casewhere a TU size is 8×8, and a sub-block size is 2×8. The method in whichcoefficients are scanned diagonally in the vertical direction for eachline in the units of 2×8 sub-blocks (longitudinally long sub-blocks)illustrated in FIG. 15(b) is suitable for a case where coefficientsconcentrate on vertical frequency components.

FIG. 15(c) illustrates an example of the up-right diagonal scan in acase where a TU size is 8×8, and a sub-block size is 4×4.

[Sub-Block Scan Order Table]

In addition, the scan order table storage unit 122 stores a sub-blockscan order for designating a scan order of sub-blocks. The sub-blockscan order is designated by a size of a process target TU (block) and ascan index scanIdx associated with a prediction mode index (predictiondirection) of an intra-prediction mode. In a case where a predictionmode method used for a process target TU is intra-prediction, thecoefficient decoding control unit 123 refers to a table which isdesignated by a size of the TU and the scan index scanIdx associatedwith a prediction mode of the TU, so as to determine a scan order ofsub-blocks.

[Coefficient Decoding Control Unit 123]

The coefficient decoding control unit 123 has a configuration forcontrolling an order of a decoding process in each constituent elementincluded in the quantized residual information decoding unit 111.

Specifically, the coefficient decoding control unit 123 performssub-block splitting, the supply of each sub-block position according toa sub-block scan order, and the supply of a position of each frequencycomponent in a sub-block according to a scan order.

The coefficient decoding control unit 123 derives a sub-block size inaccordance with a scan order and/or a TU size, and splits the TU in thederived sub-block size so as to split the TU into sub-blocks. Asplitting method is as described in FIGS. 14 and 15, and thusdescription thereof will be omitted here.

The coefficient decoding control unit 123 specifies a position of thelast non-zero transform coefficient according to the forward scan byreferring to the syntaxes last_significant_coeff_x andlast_significant_coeff_y supplied from the last coefficient positiondecoding unit 121, and supplies a position (xCG,yCG) of each sub-blockto the sub-block coefficient presence/absence flag decoding unit 127 ina backward scan order of a scan order which uses a position of asub-block including the specified position of the last non-zerotransform coefficient as a starting point and is given by the sub-blockscan order table stored in the scan order table storage unit 122. Inaddition, the coefficient decoding control unit 123 supplies a size of acorresponding TU and a scan index scanIdx associated with a predictionmode of the TU, to the coefficient presence/absence flag decoding unit124.

Further, in relation to a process target sub-block, the coefficientdecoding control unit 123 supplies a position (xC,yC) of each frequencycomponent included in the process target sub-block to the coefficientpresence/absence flag decoding unit 124 and the decoded coefficientstorage unit 126 in a backward scan order given by the scan order tablestored in the scan order table storage unit 122. Here, as a scan orderof each frequency component included in the process target sub-block, ina case of intra-prediction, a scan order (any one of the horizontal fastscan, the vertical fast scan, and the up-right diagonal scan) indicatedby a scan index scanIdx which is designated by the intra-prediction modeindex IntraPredMode and a value log 2TrafoSize for designating a TU sizemay be used, and, in a case of inter-prediction, the up-right diagonalscan may be used.

As mentioned above, the coefficient decoding control unit 123 has aconfiguration of setting a sub-block scan order and a scan order in asub-block according to a prediction direction of intra-prediction in acase where a prediction method which is applied to a process target unitdomain (a block or a TU) is the intra-prediction.

Generally, since an intra-prediction mode and a bias of a transformcoefficient are correlated with each other, a scan order is changedaccording to the intra-prediction mode, and a scan suitable for biasesof the sub-block coefficient presence/absence flag and the coefficientpresence/absence flag can be performed. Consequently, it is possible toreduce a code amount of the sub-block coefficient presence/absence flagand the coefficient presence/absence flag which are coding and decodingtargets, and thus to reduce a processing amount and to improve codingefficiency.

[Sub-Block Coefficient Presence/Absence Flag Decoding Unit 127]

The sub-block coefficient presence/absence flag decoding unit 127analyzes each Bin supplied from the bit decoding unit 132, so as todecode syntax significant_coeff_group_flag[xCG][yCG] designated by eachsub-block position (xCG,yCG). In addition, the sub-block coefficientpresence/absence flag decoding unit 127 calculates a context indexctxIdx for determining context which is used for the c130 to decode aBin of the syntax significant_coeff_group_flag[xCG][yCG]. The calculatedcontext index ctxIdx is supplied to the context recording/updating unit131. Here, the syntax significant_coeff_group_flag[xCG][yCG] takes 1 ina case where at least one non-zero transform coefficient is included ina sub-block designated by the sub-block position (xCG,yCG), and takes 0in a case where no non-zero transform coefficient is included therein. Avalue of the decoded syntax significant_coeff_group_flag[xCG][yCG] isstored in the decoded coefficient storage unit 126.

In addition, a more specific configuration of the sub-block coefficientpresence/absence flag decoding unit 127 will be described later.

[Coefficient Presence/Absence Flag Decoding Unit 124]

The coefficient presence/absence flag decoding unit 124 according to thepresent embodiment decodes syntax significant_coeff_flag[xC][yC]designated by each coefficient position (xC,yC). A value of the decodedsyntax significant_coeff_flag[xC][yC] is stored in the decodedcoefficient storage unit 126. In addition, the coefficientpresence/absence flag decoding unit 124 calculates a context indexctxIdx for determining context which is for the arithmetic code decodingunit 130 to decode a Bin of the syntax significant_coeff_flag[xC][yC].The calculated context index ctxIdx is supplied to the contextrecording/updating unit 131. A specific configuration of the coefficientpresence/absence flag decoding unit 124 will be described later.

[Coefficient Value Decoding Unit 125]

The coefficient value decoding unit 125 analyzes each Bin supplied fromthe bit decoding unit 132 so as to decode the syntaxescoeff_abs_level_greater1_flag, coeff_abs_level_greater2_flag,coeff_sign_flag, and coeff_abs_level_remaining, and derives a value of atransform coefficient (more specifically, a non-zero transformcoefficient) in a process target frequency component, on the basis ofresults of decoding the syntaxes. In addition, the context index ctxIdxused to decode the various syntaxes is supplied to the contextrecording/updating unit 131. The derived value of a transformcoefficient is stored in the decoded coefficient storage unit 126.

[Decoded Coefficient Storage Unit 126]

The decoded coefficient storage unit 126 has a configuration for storingeach value of a transform coefficient decoded by the coefficient valuedecoding unit 125. In addition, the decoded coefficient storage unit 126stores each value of the syntax significant_coeff_flag decoded by thecoefficient presence/absence flag decoding unit 124. Each value of thetransform coefficient stored in the decoded coefficient storage unit 126is supplied to the inverse quantization/inverse transform unit 13.

(Configuration Example of Sub-Block Coefficient Presence/Absence FlagDecoding Unit 127)

Hereinafter, with reference to FIG. 16, a specific configuration exampleof the sub-block coefficient presence/absence flag decoding unit 127will be described.

FIG. 16 is a block diagram illustrating a configuration example of thesub-block coefficient presence/absence flag decoding unit 127. Asillustrated in FIG. 16, the sub-block coefficient presence/absence flagdecoding unit 127 includes a sub-block coefficient presence/absence flagcontext deriving unit 127 a, a sub-block coefficient presence/absenceflag storage unit 127 b, and a sub-block coefficient presence/absenceflag setting unit 127 c.

Hereinafter, the sub-block coefficient presence/absence flag decodingunit 127 will be described by exemplifying a case where a sub-blockposition (xCG,yCG) is supplied from the coefficient decoding controlunit 123 in a backward scan order. In addition, in this case, thesub-block position (xCG,yCG) is supplied in a forward scan order in aconfiguration of a coding apparatus side corresponding to the sub-blockcoefficient presence/absence flag decoding unit 127.

(Sub-Block Coefficient Presence/Absence Flag Context Deriving Unit 127a)

The sub-block coefficient presence/absence flag context deriving unit127 a included in the sub-block coefficient presence/absence flagdecoding unit 127 derives a context index assigned to a sub-block whichis designated by each sub-block position (xCG,yCG). The context indexassigned to the sub-block is used to decode a Bin indicating the syntaxsignificant_coeff_group_flag for the sub-block. In addition, in a casewhere the context index is derived, a value of the decoded sub-blockcoefficient presence/absence flag stored in the sub-block coefficientpresence/absence flag storage unit 127 b is referred to. The sub-blockcoefficient presence/absence flag context deriving unit 127 a suppliesthe derived context index to the context recording/updating unit 131.

In the derivation of the context index assigned to a sub-block, asub-block coefficient presence/absence flag of a sub-block (xCG+1,yCG)(refer to FIG. 17(b)) located to be adjacent to the right side of thesub-block position (xCG,yCG) and a sub-block coefficientpresence/absence flag of a sub-block (xCG,yCG+1) (refer to FIG. 17(a))located on the lower side of the sub-block position (xCG,yCG) arereferred to.

In other words, the context index assigned to the sub-block is derived,specifically, by using the sub-block position (xCG,yCG), and values ofthe decoded sub-block coefficient presence/absence flags stored in thesub-block coefficient presence/absence flag storage unit 127 b.

More specifically, the context index is set as follows by referring to avalue of the decoded sub-block coefficient presence/absence flagsignificant_coeff_group_flag[xCG+1][yCG] which is decoded for thesub-block (xCG+1,yCG) located to be adjacent to the right side of thesub-block position (xCG,yCG) and a value of the decoded sub-blockcoefficient presence/absence flagsiginificant_coeff_group_flag[xCG][yCG+1] which is decoded for thesub-block (xCG,yCG+1) located on the lower side of the sub-blockposition (xCG,yCG).

ctxIdx=ctxIdxOffset+Min((significant_coeff_group_flag[xCG+1][yCG]+significant_coeff_group_flag[xCG][yCG+1]),1)

In addition, the initial value ctxIdxOffset is determined by cIdxindicating a color space. Further, in a case where a decoded sub-blocklocated at (xCG+1,yCG) or (xCG,yCG+1) is not present, a value of asub-block coefficient presence/absence flag located at (xCG+1,yCG) or(xCG,yCG+1) is treated as zero.

(Sub-Block Coefficient Presence/Absence Flag Storage Unit 127 b)

The sub-block coefficient presence/absence flag storage unit 127 bstores each value of the syntax significant_coeff_group_flag which isdecoded or is set by the sub-block coefficient presence/absence flagsetting unit 127 c. The sub-block coefficient presence/absence flagsetting unit 127 c may read the syntax significant_coeff_group_flagassigned to an adjacent sub-block from the sub-block coefficientpresence/absence flag storage unit 127 b.

(Sub-Block Coefficient Presence/Absence Flag Setting Unit 127 c)

The sub-block coefficient presence/absence flag setting unit 127 cdecodes or sets the syntax significant_coeff_group_flag[xCG][yCG] byanalyzing each Bin supplied from the bit decoding unit 132. Morespecifically, the sub-block coefficient presence/absence flag settingunit 127 c decodes or sets the syntaxsignificant_coeff_group_flag[xCG][yCG] by referring to the sub-blockposition (xCG,yCG) and the syntax significant_coeff_group_flag assignedto a sub-block (also referred to as an adjacent sub-block) adjacent to asub-block designated by the sub-block position (xCG,yCG). In addition, avalue of the decoded or set syntaxsignificant_coeff_group_flag[xCG][yCG] is supplied to the coefficientpresence/absence flag decoding unit 124.

As illustrated in FIG. 17(c), the sub-block coefficient presence/absenceflag setting unit 127 c refers to a value of the sub-block coefficientpresence/absence flag significant_coeff_group_flag[xCG+1][yCG] assignedto the sub-block (xCG+1,yCG) adjacent to the sub-block position(xCG,yCG) and a value of the sub-block coefficient presence/absence flagsignificant_coeff_group_flag[xCG][yCG+1] assigned to the sub-block(xCG,yCG+1), so as to derive a context index used to decode thesub-block coefficient presence/absence flagsignificant_coeff_group_flag[xCG][yCG+1].

In addition, in a block in which the sub-block coefficientpresence/absence flag is set to 0, the coefficient presence/absence flagcoding unit 124 can skip decoding of the coefficient presence/absenceflag significant_coeff_flag, and thus a decoding process is simplified.

With reference to FIG. 18, a specific example thereof will be described.In a case where transform coefficients are distributed as illustrated inFIG. 18(a), a sub-block coefficient presence/absence flag assigned toeach sub-block is as illustrated in FIG. 18(b). In other words, among4×4 sub-blocks, a non-zero transform coefficient is present in thesub-blocks of the first row, but a non-zero transform coefficient is notpresent in the sub-blocks of the second row and thereafter.

Therefore, in the example illustrated in FIG. 18(b), the coefficientpresence/absence flag decoding unit 124 can skip decoding of thecoefficient presence/absence flag significant_coeff_flag in decoding ofthe sub-blocks of the second row and thereafter.

<<Configuration Example of Coefficient Presence/Absence Flag DecodingUnit 124>>

Hereinafter, a specific configuration of the coefficientpresence/absence flag decoding unit 124 will be described with referenceto FIG. 1. FIG. 1 is a block diagram illustrating a configurationexample of the coefficient presence/absence flag decoding unit 124. Thecoefficient presence/absence flag decoding unit 124 includes a TU sizedetermining unit 124 a, a position context deriving unit 124 b, anadjacent sub-block coefficient presence/absence context deriving unit124 c, and a coefficient presence/absence flag setting unit 124 e.

(TU Size Determining Unit 124 a)

A position (xC,yC) of a transform coefficient which is a process targetand logarithmic values (log 2TrafoWidth and log 2TrafoHeight) of atransform block are input to the TU size determining unit 124 a. A TUsize is obtained by calculating a width and a height of a frequencydomain from the logarithmic value sizes by respectively using (1<<log2TrafoWidth) and (1<<log 2TrafoHeight). In addition, the logarithmicvalue sizes may not be used, but a width of a height of a frequencydomain may be directly input.

The TU size determining unit 124 a selects the position context derivingunit 124 b or the adjacent sub-block coefficient presence/absencecontext deriving unit 124 c according to a target TU size. The selectedcontext deriving unit derives a context index ctxIdx.

For example, in a case where a TU size is equal to or smaller than apredetermined size (for example, in a case of a 4×4 TU), the TU sizedetermining unit 124 a selects the position context deriving unit 124 b.

Therefore, the position context deriving unit 124 b derives a contextindex ctxIdx and assigns the derived context index to a decoding targetfrequency component.

On the other hand, in a case where a target TU size is larger than thepredetermined size (for example, in a case of an 8×8 TU, a 16×16 TU, ora 32×32 TU), the TU size determining unit 124 a selects the adjacentsub-block coefficient presence/absence context deriving unit 124 c.

Therefore, the adjacent sub-block coefficient presence/absence contextderiving unit 124 c derives a context index ctxIdx and assigns thederived context index to a decoding target frequency component.

In addition, the TU size determining unit 124 a is not limited to theabove-described configuration, and may have a configuration of derivinga context index ctxIdx which is common to TU sizes of a 4×4 TU to a32×32 TU. In other words, the TU size determining unit 124 a may have aconfiguration of fixedly selecting either one of the position contextderiving unit 124 b and the adjacent sub-block coefficientpresence/absence context deriving unit 124 c regardless of a TU size.

(Position Context Deriving Unit 124 b)

The position context deriving unit 124 b derives a context index ctxIdxfor a target frequency component on the basis of a position (xC,yC) ofthe target frequency component in a frequency domain. In addition, in acase where a context index ctxIdx which is a fixed value is derivedregardless of a position of a frequency component, the position contextderiving unit 124 b may perform the derivation process.

(Adjacent Sub-Block Coefficient Presence/Absence Context Deriving Unit124 c)

The adjacent sub-block coefficient presence/absence context derivingunit 124 c selects a context derivation pattern according to whether ornot a non-zero transform coefficient is present in an adjacentsub-block, and derives a context index for a decoding target frequencycomponent from coordinates of the decoding target frequency component ina sub-block according to the selected derivation pattern. Details ofExamples thereof will be described later.

(Coefficient Presence/Absence Flag Setting Unit 124 e)

The coefficient presence/absence flag setting unit 124 e analyzes eachBin supplied from the bit decoding unit 132 so as to set the syntaxsignificant_coeff_flag[xC][yC]. The setsyntaxsignificant_coeff_flag[xC][yC] is supplied to the decodedcoefficient storage unit 126.

In a case where a target frequency domain is split into sub-blocks, thecoefficient presence/absence flag setting unit 124 e refers to thesyntax significant_coeff_group_flag[xCG][yCG] assigned to a targetsub-block, and sets significant_coeff_flag[xC][yC] for all frequencycomponents included in the target sub-block to 0 in a case where a valueof significant_coeff_group_flag[xCG][yCG] is 0.

<<Examples: Minimization of Change in Context Index>>

Hereinafter, specific Examples of the adjacent sub-block coefficientpresence/absence context deriving unit 124 c will be described.

Specifically, the adjacent sub-block coefficient presence/absencecontext deriving unit 124 c derives context index sigCtx as follows.

First, the adjacent sub-block coefficient presence/absence contextderiving unit 124 c refers to the right adjacent sub-block illustratedin FIG. 17(b) and the lower adjacent sub-block illustrated in FIG.17(a), and obtains a pattern index idxCG which is an index forspecifying a context derivation pattern, from the sub-block coefficientpresence/absence flag in each of the adjacent sub-blocks, by using thefollowing Equation (A).

idxCG=significant_coeff_group_flag[xCG+1][yCG]+(significance_coeff_group_flag[xCG][yCG+1]<<1)  (A)

in the above Equation (A), significant_coeff_group_flag is a flagindicating that at least one non-zero transform coefficient is presentin a sub-block as described above. In a case where at least one non-zerotransform coefficient is present in a sub-block, a value of at least onenon-zero transform coefficient is present in a sub-block is “1”, and ina case where no non-zero transform coefficient is present in asub-block, a value of at least one non-zero transform coefficient ispresent in a sub-block is “0”.

significant_coeff_group_flag[xCG+1][yCG] indicates a value of a decodedsub-block coefficient presence/absence flag which is decoded for thesub-block (xCG+1,yCG) located to be adjacent to the right side of thesub-block position (xCG,yCG), andsiginificant_coeff_group_flag[xCG][yCG+1]

indicates a value of a decoded sub-block coefficient presence/absenceflag which is decoded for the sub-block (xCG,yCG+1) located on the lowerside of the sub-block position (xCG,yCG).

On the basis of the above Equation (A), the pattern index idxCG takesvalues of 0 to 3 in the following patterns 0 to 3, respectively.

(Pattern 0)

In a case where a value of the sub-block coefficient presence/absenceflag is 0 in both of the right adjacent sub-block (xCG+1,yCG) and thelower adjacent sub-block (xCG,yCG+1)

(Pattern 1)

In a case where a value of the sub-block coefficient presence/absenceflag is 1 in the right adjacent sub-block (xCG+1,yCG), and a value ofthe sub-block coefficient presence/absence flag is 0 in the loweradjacent sub-block (xCG,yCG+1)

(Pattern 2)

In a case where a value of the sub-block coefficient presence/absenceflag is 0 in the right adjacent sub-block (xCG,yCG+1), and a value ofthe sub-block coefficient presence/absence flag is 1 in the loweradjacent sub-block (xCG,yCG+1)

(Pattern 3)

In a case where a value of the sub-block coefficient presence/absenceflag is 1 in both of the right adjacent sub-block (xCG+1,yCG) and thelower adjacent sub-block (xCG,yCG+1)

Next, the adjacent sub-block coefficient presence/absence contextderiving unit 124 c derives a context index for a decoding targetfrequency component from coordinates (xB,yB) of the decoding targetfrequency component in a sub-block according to the pattern index idxCGobtained by using the above Equation (A).

In addition, the coordinates (xB,yB) in the sub-block may be derived byusing a coefficient position (xC,yC) and a sub-block position (xCG,yCG)in a TU. In other words, the coordinates (xB,yB) in the sub-block may bederived by using xB=xC−(xCG<<2) and yB=yC−(yCG<<2). Further, thecoordinates (xB,yB) in the sub-block may also be derived by a logicalsum of a bit unit using an operator of the coefficient position (xC,yC)in a TU and “3”. That is, the coordinates (xB,yB) may be obtained bycomputing xB=xC&3 and yB=yC&3.

With reference to FIGS. 19 and 20, a description will be made of amethod in which the adjacent sub-block coefficient presence/absencecontext deriving unit 124 c derives a context index.

FIG. 19 is a diagram illustrating an example of a pseudo-code forderiving a context index from coordinates of a process target frequencycomponent in a sub-block according to a pattern index idxCG. Withreference to FIG. 19, a description will be made of a value of a contextindex which is derived in each case of patterns 0 to 3. In addition, thenotation of a form of x?y:z indicates the following logical operation.In other words, “if x is “true” or is “not 0””, a value of y isevaluated, and otherwise, a value of z is evaluated. This is also thesame for the following.

(Case of Pattern 0)

In a case of the pattern 0, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index byusing sigCtx=(xB+yB<=2) ? 1:0.

Therefore, in a case of the pattern 0, if a sum of the coordinate xB inthe horizontal direction of the coordinates (xB,yB) in the sub-block andthe coordinate yB in the vertical direction is equal to or smaller than2, a value of a context index is “1”, and, otherwise, a value of acontext index is “0”.

Consequently, values of the context indexes are arranged as illustratedin FIG. 20(a).

In addition, in the pattern 0, a context index may be derived by usingsigCtx=(xB+yB<3) ? 1:0.

Further, in the context index, sigCtx=0 corresponds to a case where anoccurrence probability of a non-zero transform coefficient is low, andsigCtx=2 corresponds to a case where an occurrence probability of anon-zero transform coefficient is high. Furthermore, sigCtx=1corresponds to a case where an occurrence probability of a non-zerotransform coefficient is intermediate between a high case and a lowcase. Moreover, in the above example, description has been made thatsigCtx=0 corresponds to a case where an occurrence probability of anon-zero transform coefficient is low, and sigCtx=2 corresponds to acase where an occurrence probability of a non-zero transform coefficientis high, but the present invention is not limited thereto.Alternatively, values of context indexes may be set so that sigCtx=2corresponds to a case where an occurrence probability of a non-zerotransform coefficient is low, and sigCtx=0 corresponds to a case wherean occurrence probability of a non-zero transform coefficient is high,and the same applies to the following Examples. In other words, in thefollowing Examples, for analysis, a value of “2” of a context indexcorresponding to each of coordinates in a sub-block in each indexpattern idxCG may be replaced with “0”, and a value of “0” of a contextindex corresponding to each of coordinates in a sub-block in each indexpattern idxCG may be replaced with “2”.

(Case of Pattern 1)

In a case of the pattern 1, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index onthe basis of a table tb11 in which coordinates (xB,yB) in a sub-block iscorrelated with a context index.

As exemplified in FIG. 19, the table tb11 is an arrangement includingsixteen elements such as {1, 1, 1, 1, 1, 1, 1, 0, 1, 0, 0, 0, 0, 0, 0,0}.

The adjacent sub-block coefficient presence/absence context derivingunit 124 c derives a context index by using sigCtx=tb11[xB+(yB<<2)] onthe basis of the table tb11.

Therefore, values of the context indexes are arranged as illustrated inFIG. 20(b). In other words, the first to fourth elements of thearrangement respectively correspond to (0,0) to (3,0) of the first rowin the sub-block illustrated in FIG. 20(b). In the following, similarly,the fifth to eighth elements, the ninth to twelfth elements, and thethirteenth to sixteenth elements of the arrangement respectivelycorrespond to the second row, the third row, and the fourth row.

(Case of Pattern 2)

In a case of the pattern 2, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index onthe basis of a table tb12 in which coordinates (xB,yB) in a sub-block iscorrelated with a context index.

As exemplified in FIG. 19, the table tb12 is an arrangement includingsixteen elements such as {1, 1, 1, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 0, 0,0}.

The adjacent sub-block coefficient presence/absence context derivingunit 124 c derives a context index by using sigCtx=tb12[xB+(yB<<2)] onthe basis of the table tb12.

Therefore, values of the context indexes are arranged as illustrated inFIG. 20(c). In other words, a correspondence between the elements of thearrangement and the coordinates in the sub-block illustrated in FIG.20(c) is the same as in a case of the pattern 1. For example, the firstto fourth elements of the arrangement respectively correspond to (0,0)to (3,0) of the first row in the sub-block illustrated in FIG. 20(b).

(Case of Pattern 3)

In a case of the pattern 3, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index byusing sigCtx=(xB+yB<=4) ? 2:1.

Therefore, in a case of the pattern 3, if a sum of the coordinate xB inthe horizontal direction of the coordinates (xB,yB) in the sub-block andthe coordinate yB in the vertical direction is 4 or less, a value of acontext index is “2”, and, otherwise, a value of a context index is “1”.

Consequently, values of the context indexes are arranged as illustratedin FIG. 20(d).

In addition, in the pattern 3, a context index may be derived by usingsigCtx=(xB+yB<5) ? 2:1. Hereinafter, whether the determination isperformed in “x or less” or “x+1 below” may be changed as appropriate.

Here, advantages of the configuration will be described throughcomparison with a comparative example according to the related art.

First, a scan order in a sub-block is assumed to be the up-rightdiagonal scan as illustrated in FIG. 21. In addition, the scan orderillustrated in FIG. 21 is a forward direction.

Decoding of transform coefficients is performed in a backward scan orderfrom “15” to “0” illustrated in FIG. 21.

(Configuration Related to Comparative Example)

Hereinafter, a configuration illustrated in FIGS. 51 and 52 is used as acomparative example. In the configuration related to the comparativeexample, if context indexes are arranged in a backward scan order ineach of the patterns 0 to 3, this leads to the following sequences.

Pattern 0: 0000000000111111

Pattern 1: 0001001100110111

Pattern 2: 0000010011011111

Pattern 3: 1112222222222222

Here, the pattern 1 and the pattern 2 have a large number of changesfrom “0” to “1” or from “1” to “0”.

Specifically, in the pattern 1, the number of changes from “0” to “1” isfour, the number of changes from “1” to “0” is three, and thus a totalof seven changes occur.

In addition, in the pattern 2, the number of changes from “0” to “1” isthree, the number of changes from “1” to “0” is two, and thus a total offive changes occur.

Among items of hardware, there is hardware which defines the number ofrepeated 0s and the number of repeated 1s, and derives a context indexcorresponding to a position in a sub-block according to the definition.In such hardware, if the number of changes in 0s and 1s increases,complexity of a configuration required to realize the hardware alsoincreases.

(Configuration Related to Example)

As mentioned above, the moving image decoding apparatus 1 related to thepresent example includes an arithmetic decoding device which decodescoded data which is obtained by arithmetically coding various syntaxesindicating a transform coefficient with respect to each transformcoefficient which is obtained for each frequency component by performingfrequency transform on a target image for each unit domain. Thearithmetic decoding device includes sub-block splitting means forsplitting a target frequency domain corresponding to a process targetunit domain into sub-blocks each having a 4×4 size according to apredetermined definition; sub-block coefficient presence/absence flagdecoding means for decoding a sub-block coefficient presence/absenceflag indicating whether or not at least one non-zero transformcoefficient is included in the sub-block with respect to the respectivesub-blocks into which the frequency domain is split by the sub-blocksplitting means; directivity determining means for determining adirectivity of a distribution of transform coefficients on the basis ofa sub-block coefficient presence/absence flag in a sub-block adjacent toa process target sub-block; and context index deriving means forderiving a context index assigned to a transform coefficientpresence/absence flag which is syntax indicating whether or not theprocess target transform coefficient is 0, in which, in a case where ascan order applied to the sub-block is the up-right diagonal scan, adetermined directivity is a vertical direction, and coordinates of thesub-block having the 4×4 size are set to (xB,yB) (where xB is acoordinate in a horizontal direction, yB is a coordinate in a verticaldirection, and the upper left side of the sub-block is set to an origin(0,0)), the context index deriving means derives the context indexcorresponding to a case where an occurrence probability of a transformcoefficient is higher than in domains other than a domain formed by(0,0) to (0,3), (1,0) to (1,2), and (2,0).

In addition, as mentioned above, the moving image decoding apparatus 1related to the present example includes an arithmetic decoding devicewhich decodes coded data which is obtained by arithmetically codingvarious syntaxes indicating a transform coefficient with respect to eachtransform coefficient which is obtained for each frequency component byperforming frequency transform on a target image for each unit domain.The arithmetic decoding device includes sub-block splitting means forsplitting a target frequency domain corresponding to a process targetunit domain into sub-blocks each having a 4×4 size according to apredetermined definition; sub-block coefficient presence/absence flagdecoding means for decoding a sub-block coefficient presence/absenceflag indicating whether or not at least one non-zero transformcoefficient is included in the sub-block with respect to the respectivesub-blocks into which the frequency domain is split by the sub-blocksplitting means; directivity determining means for determining adirectivity of a distribution of transform coefficients on the basis ofa sub-block coefficient presence/absence flag in a sub-block adjacent toa process target sub-block; and context index deriving means forderiving a context index assigned to a transform coefficientpresence/absence flag which is syntax indicating whether or not theprocess target transform coefficient is 0, in which, in a case where ascan order applied to the sub-block is the up-right diagonal scan, adetermined directivity is a horizontal direction, and coordinates of thesub-block having the 4×4 size are set to (xB,yB) (where xB is acoordinate in a horizontal direction, yB is a coordinate in a verticaldirection, and the upper left side of the sub-block is set to an origin(0,0)), the context index deriving means derives the context indexcorresponding to a case where an occurrence probability of a transformcoefficient is higher than in domains other than a domain formed by(0,0) to (3,0), (0,1) to (2,1), and (0,2).

According to the adjacent sub-block coefficient presence/absence contextderiving unit 124 c related to the present example, sequences of contextindexes in a backward scan order in patterns 1 and 2 is as follows.

Pattern 1: 0000001100111111

Pattern 2: 0000000011111111

In the pattern 1, the number of changes from “0” to “1” is two, thenumber of changes from “1” to “0” is one, and thus the number of changesis a total of three.

In the pattern 2, the number of changes is only one from “0” to “1”.

According to the configuration, it is possible to considerably reducethe number of changes when compared with the configuration related tothe comparative example. The number of changes is at most three in thepattern 1, and is one corresponding to the minimum value in the pattern2.

As mentioned above, according to the configuration, it is possible tominimize variations (changes) in context indexes in a sub-block.Accordingly, as described above, in hardware which defines the number ofrepeated 0s and 1s, mounting of the hardware is simplified.

In addition, in a case where a process is performed in a forward scandirection, sequences which are opposite to the sequences of the pattern1 and the pattern 2 are obtained. Therefore, also in a case where aprocess is performed in the forward scan direction, the same effect canbe achieved.

MODIFICATION EXAMPLES

Modification examples of the present invention will be described below.

Modification Example 1: Minimization of Changes in Context Indexes 2

Hereinafter, a description will be made of a modification example ofchanging a scan order in a target sub-block in accordance with whetheror not a non-zero transform coefficient is present in an adjacentsub-block with reference to FIG. 22.

In the present modification example, the coefficient decoding controlunit 123 performs the supply of a position of each frequency componentaccording to a scan order in a sub-block on the basis of scan orders asillustrated in FIGS. 22(a) to 22(d).

In addition, in FIGS. 22(a) to 22(e), all arrows indicating the scanorders are illustrated in a forward direction, but a decoding process oftransform coefficients is performed in a backward scan direction whichis opposite to the directions of the arrows.

In addition, in the following, as an example, the arrangement of thecontext indexes illustrated in FIGS. 51 and 52 is used.

Hereinafter, patterns 0 to 3 will be sequentially described.

In a case of the pattern 0, as illustrated in FIG. 22 (a), thecoefficient decoding control unit 123 applies the up-right diagonal scanthereto.

In a case of the pattern 1, as illustrated in FIG. 22(b), thecoefficient decoding control unit 123 applies the horizontal fast scanthereto. That is, in a case of(significant_coeff_group_flag[xCG+1][yCG],significant_coeff_group_flag[xCG][yCG+1])=(1,0), the coefficientdecoding control unit 123 applies the horizontal fast scan thereto.

In a case of the pattern 2, as illustrated in FIG. 22 (c), thecoefficient decoding control unit 123 applies the vertical fast scanthereto. That is, in a case of(significant_coeff_group_flag[xCG+1][yCG],significant_coeff_group_flag[xCG][yCG+1])=(0,1), the coefficientdecoding control unit 123 applies the vertical fast scan thereto.

In a case of the pattern 3, as illustrated in FIG. 22 (d), thecoefficient decoding control unit 123 applies the up-right diagonal scanthereto.

[Operations and Effects]

As described above, the moving image decoding apparatus 1 related toModification Example 1 includes an arithmetic decoding device whichdecodes coded data which is obtained by arithmetically coding varioussyntaxes indicating a transform coefficient with respect to eachtransform coefficient which is obtained for each frequency component byperforming frequency transform on a target image for each unit domain.The arithmetic decoding device includes sub-block splitting means forsplitting a target frequency domain corresponding to a process targetunit domain into sub-blocks each having a predetermined size; sub-blockcoefficient presence/absence flag decoding means for decoding asub-block coefficient presence/absence flag indicating whether or not atleast one non-zero transform coefficient is included in the sub-blockwith respect to the respective sub-blocks into which the frequencydomain is split by the sub-block splitting means; directivitydetermining means for determining a directivity of a distribution oftransform coefficients on the basis of a sub-block coefficientpresence/absence flag in a sub-block adjacent to a process targetsub-block; and transform coefficient decoding means for decoding thetransform coefficients by using a scan order according to a directivitydetermined by the directivity determining means.

According to the configuration, in a case (FIG. 22(b)) where there is ahigh probability that non-zero transform coefficients concentrates inthe horizontal direction, the horizontal fast scan is applied thereto,and, in a case (FIG. 22(c)) where there is a high probability thatnon-zero transform coefficients concentrates in the vertical direction,the vertical fast scan is applied thereto.

Accordingly, a scan can be performed in an order of a higher appearingprobability of non-zero transform coefficients, and thus it is possibleto improve coding efficiency.

In addition, sequences of context indexes in a backward scan order areas follows.

Pattern 0:0000000000111111

Pattern 1:0000000011111111

Pattern 2:0000000011111111

Pattern 3:1112222222222222

Accordingly, the number of changes in 0s and 1s of the context indexesis at most one in the backward scan order in a sub-block.

In addition, in the above description, the up-right diagonal scan isused in the patterns 0 and 3, but, alternatively, a zigzag scan asillustrated in FIG. 22(e) may be used. Further, the above-described scanorder may be stored in the scan order table storage unit 122.

Modification Example 2: Reduction in Derivation Pattern

Hereinafter, with reference to FIGS. 23 and 24, a description will bemade of a modification example in which context derivation patterns arechanged in accordance with the number of non-zero transform coefficientswhich are present in an adjacent sub-block.

In the present modification example, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c obtains a pattern indexidxCG which is an index for specifying a context derivation pattern fromsub-block coefficient presence/absence flags in adjacent sub-blocks(right adjacent and lower adjacent sub-blocks), by using the followingEquation (B).

idxCG=significant_coeff_group_flag[xCG+1][yCG]+significant_coeff_group_flag[xCG][yCG+1]  (B)

On the basis of the above Equation (B), the pattern index idxCG takesvalues of 0 to 2 in the following patterns 0 to 2, respectively.

(Pattern 0) In a case where a value of the sub-block coefficientpresence/absence flag is 0 in both of the right adjacent sub-block(xCG+1,yCG) and the lower adjacent sub-block (xCG,yCG+1)

(Pattern 1) In a case where a value of the sub-block coefficientpresence/absence flag is 1 in one of the right adjacent sub-block(xCG+1,yCG) and the lower adjacent sub-block (xCG,yCG+1), and a value ofthe sub-block coefficient presence/absence flag is 0 in the otherthereof

(Pattern 2) In a case where a value of the sub-block coefficientpresence/absence flag is 1 in both of the right adjacent sub-block(xCG+1,yCG) and the lower adjacent sub-block (xCG,yCG+1)

In addition, in the present modification example, the adjacent sub-blockcoefficient presence/absence context deriving unit 124 c derives acontext index in a method illustrated in FIG. 23.

FIG. 23 is a diagram illustrating another example of a pseudo-code forderiving a context index from coordinates of a process target frequencycomponent in a sub-block according to a pattern index idxCG obtainedfrom Equation (B).

With reference to FIG. 23, a description will be made of a value of acontext index which is derived in each case of a patterns 0 to 3.

(Case of Pattern 0)

In a case of the pattern 0, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index byusing sigCtx=(xB+yB<=2) ? 1:0.

In other words, a case of the pattern 0 is the same as a case of thepattern 0 of the above-described example. Therefore, values of thecontext indexes are arranged as illustrated in FIG. 24(a).

(Case of Pattern 1)

In a case of the pattern 1, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index byusing sigCtx=(xB+yB<3) ? 1:0.

Therefore, in a case of the pattern 1, if a sum of the coordinate xB inthe horizontal direction of the coordinates (xB,yB) in the sub-block andthe coordinate yB in the vertical direction is 3 or less, a value of acontext index is “1”, and, otherwise, a value of a context index is “0”.

Consequently, values of the context indexes are arranged as illustratedin FIG. 24(b).

(Case of Pattern 2)

In a case of the pattern 2, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index byusing sigCtx=(xB+yB<4) ? 2:1.

In other words, a case of the pattern 2 is the same as a case of thepattern 3 of the above-described example. Therefore, values of thecontext indexes are arranged as illustrated in FIG. 24(c).

Modification Example 2-1

Hereinafter, with reference to FIGS. 54 and 55, a description will bemade of a modification example of using a context index derivationmethod having three stages in relation to the pattern 0 and the pattern1 of Modification Example 2. In the arrangement of values of the contextindexes related to Modification Example 2, values of two stages aretaken in each pattern so that sigCtx=0 or 1 in the patterns 0 and 1(FIGS. 24(a) and 24(b)), and sigCtx=1 or 2 in the pattern 2 (FIG.24(c)). By increasing these stages, it is possible to realize anarrangement of values of context indexes which are more suitable foractual occurrence circumstances of a transform coefficient. FIG. 54illustrates a pseudo-code for deriving a context index from coordinatesof a process target frequency component in a sub-block according to apattern index idxCG obtained from the above Equation (B), related toModification Example 2-1. FIG. 55 illustrates arrangements of values ofthe context indexes in the context index derivation method using thepseudo-code illustrated in FIG. 54.

In addition, Modification Example 2-1 may be said to be a combination ofModification Example 2 related to reduction in a derivation pattern withModification Example 5 described later.

(Case of Pattern 0)

In a case of the pattern 0, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index asfollows according to a value of xB+yB.

In a case where xB+yB is equal to or smaller than TH1, the adjacentsub-block coefficient presence/absence context deriving unit 124 cderives sigCtx=2. In addition, in a case where xB+yB is greater than TH1and is equal to or smaller than TH2, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives sigCtx=1. In othercases, the adjacent sub-block coefficient presence/absence contextderiving unit 124 c derives sigCtx=0. Here, if the threshold valueTH1=0, and the threshold value TH2=2, values of context indexes arearranged as illustrated in FIG. 55(a).

(Case of Pattern 1)

In a case of the pattern 1, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index asfollows according to a value of xB+yB.

In a case where xB+yB is equal to or smaller than TH3, the adjacentsub-block coefficient presence/absence context deriving unit 124 cderives sigCtx=2. In addition, in a case where xB+yB is greater than TH3and is equal to or smaller than TH4, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives sigCtx=1. In othercases, the adjacent sub-block coefficient presence/absence contextderiving unit 124 c derives sigCtx=0. Here, if the threshold value TH3=1and the threshold value TH4=3, values of context indexes are arranged asillustrated in FIG. 55(b).

(Case of Pattern 2)

As an example, a threshold value TH5 is set to 4. If the threshold valueTH5=4, this leads to the same result as in the pattern 2 (FIG. 24(c)) ofModification Example 2, and thus description thereof will be omitted.

In addition, the threshold values TH1, TH2, TH3, and TH4 are preferablyset to satisfy TH1<TH3, and TH2<TH4, in consideration of biases ofoccurrence probabilities of a non-zero transform coefficient in therespective patterns.

From the test performed by the present inventor, it has been confirmedthat Modification Example 2-1 can further improve coding efficiency thanModification Example 2, especially, in an intra-prediction block. Inrelation to the elements of Modification Example 2-1, in the pattern 0and the pattern 1, a value of a context index located at a firstdistance (the pattern 0: xB+yB<=TH1, and the pattern 1: xB+yB<=TH3) fromthe upper rightmost part is set to 2 which indicates an occurrenceprobability is high, a value of a context index located at a seconddistance (the pattern 0: TH1<xB+yB<=TH2, and the pattern 1:TH3<xB+yB<=TH4) from the first distance is set to 1 which indicates anoccurrence probability is intermediate, and a value of a context indexlocated at other positions is set to 0 which indicates an occurrenceprobability is low.

In addition, in relation of the threshold value TH5, the threshold valueTH5 may be set to satisfy TH4<TH5 as described above.

[Operations and Effects]

As described above, the moving image decoding apparatus 1 related toModification Example 2 includes an arithmetic decoding device whichdecodes coded data which is obtained by arithmetically coding varioussyntaxes indicating a transform coefficient with respect to eachtransform coefficient which is obtained for each frequency component byperforming frequency transform on a target image for each unit domain.The arithmetic decoding device includes sub-block splitting means forsplitting a target frequency domain corresponding to a process targetunit domain into sub-blocks each having a predetermined size; sub-blockcoefficient presence/absence flag decoding means for decoding asub-block coefficient presence/absence flag indicating whether or not atleast one non-zero transform coefficient is included in the sub-blockwith respect to the respective sub-blocks into which the frequencydomain is split by the sub-block splitting means;coefficient-present-sub-block number counting means for counting thenumber of sub-blocks including at least one non-zero transformcoefficient for each sub-block adjacent to a process target sub-block onthe basis of the sub-block coefficient presence/absence flag; andcontext index deriving means for deriving a context index assigned to atransform coefficient presence/absence flag which is syntax indicatingwhether or not the transform coefficient is 0, in which the contextindex deriving means derives the context index by using a sum of acoordinate in a horizontal direction and a coordinate in a verticaldirection of a process target transform coefficient in the processtarget sub-block according to the number counted by thecoefficient-present-sub-block number counting means.

In the configuration, the sub-block coefficient presence/absence flag isnot differentiated between a right adjacent sub-block and a loweradjacent sub-block.

Accordingly, when compared with the above-described Example, it ispossible to reduce the number of context derivation patterns. Inaddition, the comparisons in the respective patterns are all performedthrough a comparison between “xB+yB” and a predetermined thresholdvalue. Further, the arrangements illustrated in FIGS. 24(a) to 24(c) arerelated to the up-right diagonal scan, the number of changes in contextindexes in a scan order in a sub-block is only one, and thus mountingthereof in hardware is simplified.

The moving image decoding apparatus related to Modification Example 2-1described above includes an arithmetic decoding device which decodescoded data which is obtained by arithmetically coding various syntaxesindicating a transform coefficient with respect to each transformcoefficient which is obtained for each frequency component by performingfrequency transform on a target image for each unit domain. Thearithmetic decoding device includes sub-block splitting means forsplitting a target frequency domain corresponding to a process targetunit domain into sub-blocks each having a predetermined size; sub-blockcoefficient presence/absence flag decoding means for decoding asub-block coefficient presence/absence flag indicating whether or not atleast one non-zero transform coefficient is included in the sub-blockwith respect to the respective sub-blocks into which the frequencydomain is split by the sub-block splitting means;coefficient-present-sub-block number counting means for counting thenumber of sub-blocks including at least one non-zero transformcoefficient for each sub-block adjacent to a process target sub-block onthe basis of the sub-block coefficient presence/absence flag; andcontext index deriving means for deriving a context index assigned to atransform coefficient presence/absence flag which is syntax indicatingwhether or not the transform coefficient is 0, in which the contextindex deriving means derives the context indexes respectivelycorresponding to a case where an occurrence probability of a non-zerotransform coefficient is low, a case where an occurrence probability ofa non-zero transform coefficient is high, and a case where an occurrenceprobability of a non-zero transform coefficient is intermediate betweenthe high case and the low case, on the basis of a position of a processtarget transform coefficient in the process target sub-block, by using asum of a coordinate in a horizontal direction and a coordinate in avertical direction of a process target transform coefficient in theprocess target sub-block according to the number counted by thecoefficient-present-sub-block number counting means.

In the configuration, the sub-block coefficient presence/absence flag isnot differentiated between a right adjacent sub-block and a loweradjacent sub-block.

Accordingly, when compared with the above-described Example, it ispossible to reduce the number of context derivation patterns. Inaddition, the comparisons in the respective patterns are all performedthrough a comparison between “xB+yB” and a predetermined thresholdvalue. Further, the arrangements illustrated in FIGS. 55(a) and 55(b)are related to the up-right diagonal scan, the number of changes incontext indexes in a scan order in a sub-block is only two, and thusmounting thereof in hardware is simplified.

In addition, in a case where it is determined that no non-zero transformcoefficient is present in two or more sub-blocks adjacent to the processtarget sub-block, the context index deriving means derives the contextindexes respectively corresponding to a case where an occurrenceprobability of a non-zero transform coefficient is low, a case where anoccurrence probability of a non-zero transform coefficient is high, anda case where an occurrence probability of a non-zero transformcoefficient is intermediate between the high case and the low case, onthe basis of a position of a process target transform coefficient in theprocess target sub-block, according to the determination result, and canimprove coding efficiency. Particularly, a case where an occurrenceprobability of a non-zero transform coefficient is high is preferablyassigned to an upper left position in the process target sub-block.

Further, in a case where it is determined that one or more non-zerotransform coefficients are present in one or more sub-blocks adjacent tothe process target sub-block, and no non-zero transform coefficient ispresent in one or more sub-blocks, the context index deriving meansderives the context indexes respectively corresponding to a case wherean occurrence probability of a non-zero transform coefficient is low, acase where an occurrence probability of a non-zero transform coefficientis high, and a case where an occurrence probability of a non-zerotransform coefficient is intermediate between the high case and the lowcase, on the basis of a position of a process target transformcoefficient in the process target sub-block, according to thedetermination result, and can improve coding efficiency. Particularly,it is determined that a non-zero transform coefficient is present in aright or low adjacent sub-block, and a case where an occurrenceprobability of a non-zero transform coefficient is high is preferablyassigned to the first column and the second column in a diagonaldirection from the upper left part in the process target sub-block. Inaddition, a case where an occurrence probability of a non-zero transformcoefficient is intermediate is preferably assigned to the third columnand the fourth column in a diagonal direction from the upper left partin the process target sub-block.

As mentioned above, according to Modification Example 2-1, it ispossible to realize a context derivation pattern which is more suitablefor an actual occurrence probability of a transform coefficient than inModification Example 2, and thus it is possible to improve codingefficiency.

Modification Example 3: 2×2 Pattern

Coordinates of a sub-block having a 4×4 size takes value of 0 to 3 (2bits) in each of an X coordinate and a Y coordinate. Hereinafter, withreference to FIGS. 25 and 26, a description will be made of amodification example in which a context index is derived without usinglower bits of sub-block coordinates. In other words, in the followingmodification example, a context index is derived in the unit of a 2×2size.

In the present modification example, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c obtains a pattern indexidxCG by using the above Equation (A), and also derives a context indexin a method illustrated in FIG. 25 according to patterns 0 to 3 obtainedtherefrom.

FIG. 25 is a diagram illustrating still another example of a pseudo-codefor deriving a context index from coordinates of a process targetfrequency component in a sub-block according to a pattern index idxCGobtained from Equation (A). FIG. 26 illustrates arrangements of valuesof context indexes in the context index derivation method using thepseudo-code illustrated in FIG. 25.

With reference to FIGS. 25 and 26, a description will be made of a valueof a context index which is derived in each case of patterns 0 to 3.

(Case of Pattern 0)

In a case of the pattern 0, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index byusing sigCtx=((xB>>1)+(yB>>1)<=0) ? 1:0.

Consequently, values of the context indexes are arranged as illustratedin FIG. 26(a). In other words, as illustrated in FIG. 26(a), in a casewhere the sub-block is split into four partial domains including anupper left domain, an upper right domain, a lower left domain, and alower right domain, each having a 2×2 size, values of the contextindexes are 1 in the upper left partial domain, and values of thecontext indexes are 0 in the other partial domains.

(Case of Pattern 1)

In a case of the pattern 1, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index byusing sigCtx=((yB>>1)<=0) ? 1:0.

Consequently, values of the context indexes are arranged as illustratedin FIG. 26(a). In other words, as illustrated in FIG. 26(b), values ofthe context indexes are 1 in upper left and upper right partial domainsin the sub-block, and values of the context indexes are 0 in lower leftand lower right partial domains.

(Case of Pattern 2)

In a case of the pattern 2, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index byusing sigCtx=((xB>>1)<=0) ? 1:0.

Consequently, values of the context indexes are arranged as illustratedin FIG. 26(c). In other words, as illustrated in FIG. 26(c), values ofthe context indexes are 1 in upper left and lower left partial domainsin the sub-block, and values of the context indexes are 0 in upper rightand lower right partial domains.

(Case of Pattern 3)

In a case of the pattern 3, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index byusing sigCtx=((xB>>1)+(yB>>1)<=1) ? 2:1.

Consequently, values of the context indexes are arranged as illustratedin FIG. 26(d). In other words, as illustrated in FIG. 26(d), values ofthe context indexes are 2 in upper left, upper right and lower leftpartial domains in the sub-block, and values of the context indexes are0 in a lower right partial domain.

The context index derivation method for the moving image decodingapparatus 1 related to Modification Example 3 is a method in which alower 1 bit of coordinates (xB,yB) in a sub-block is not referred to asillustrated in FIG. 25. In addition, in an arrangement of values of thecontext indexes related to Modification Example 3, values of the contextindexes in a smaller block (here, a 2×2 block) forming a sub-block areequally obtained as illustrated in FIG. 26.

[Operations and Effects]

As mentioned above, the moving image decoding apparatus 1 related to theModification Example 3 includes an arithmetic decoding device whichdecodes coded data which is obtained by arithmetically coding varioussyntaxes indicating a transform coefficient with respect to eachtransform coefficient which is obtained for each frequency component byperforming frequency transform on a target image for each unit domain.The arithmetic decoding device includes sub-block splitting means forsplitting a target frequency domain corresponding to a process targetinto sub-blocks each having a 4×4 size according to a predetermineddefinition; sub-block coefficient presence/absence flag decoding meansfor decoding a sub-block coefficient presence/absence flag indicatingwhether or not at least one non-zero transform coefficient is includedin the sub-block with respect to the respective sub-blocks into whichthe frequency domain is split by the sub-block splitting means; patterndetermining means for determining a pattern of a value of a sub-blockcoefficient presence/absence flag which is decoded for each sub-blockadjacent to a process target sub-block; and context index deriving meansfor deriving a context index assigned to a transform coefficientpresence/absence flag which is syntax indicating whether or not theprocess target transform coefficient is 0, in which the context indexderiving means derives the context index by using higher-order bits (in2-bit expression) of each of coordinates in a horizontal direction and avertical direction of a process target transform coefficient in theprocess target sub-block according to a determination result from thepattern determining means.

According to the configuration, it is possible to perform a contextindex deriving process from input information of higher bits (4 bits).Specifically, the 4 bits are a total of 4 bits including a higher bit (1bit) of a X coordinate in a sub-block, a higher bit (1 bit) of a Ycoordinate in the sub-block, a sub-block coefficient presence/absenceflag (1 bit) in an adjacent sub-block in the X direction, and asub-block coefficient presence/absence flag (1 bit) in an adjacentsub-block in the Y direction.

In addition, since derivation of output of 0 to 2 (2 bits) from input of4 bits is preferable, a context index deriving process can be performedthrough a simple bit calculation. Detailed description thereof will bemade as follows.

First, x1, y1, x2, and y2 (each of which is 1 bit) are defined asfollows.

x1=xB=(xC−(xCG<<2))>>1

y1=yB=(yC−(yCG<<2))>>1

x2=signifcanet_coeff_group_flag[xCG+1][yCG]

y2=significant_coeff_group_flag[xCG][yCG+1]

In this case, a context index deriving process can be performed throughthe following logical calculation.

sigCtx=((x2 & y2) & ((y2 & ! y1)|(x2 & ! x1))<<1)|((x2 & y2)& (x1 &y1))|(! x2 & ! y2) & (! x1 & ! y1)|(! x2 & y2 & ! x1)|(y2 & ! x2 & ! y1)

Consequently, it is possible to exclude conditional branch from thecontext index deriving process.

Modification Example 4: 2×2 Pattern 2

Hereinafter, with reference to FIG. 27, a description will be made of amodification example of using a scan order in the 2×2 unit as a scanorder in a target sub-block.

In the present modification example, the coefficient decoding controlunit 123 performs the supply of a position of each frequency componentaccording to a scan order in a sub-block on the basis of scan orders asillustrated in FIGS. 27(a) and 27(b).

In addition, in FIGS. 22(a) to 22(e), all arrows indicating the scanorders are illustrated in a forward direction, but a decoding process oftransform coefficients is performed in a backward scan direction whichis opposite to the directions of the arrows. Further, an arrangement ofcontext indexes is not limited to ones illustrated in FIGS. 51 and 52,and may be arbitrarily set.

As illustrated in FIG. 27(a), the coefficient decoding control unit 123may set a scan order in the partial domain units in a sub-block to ascan order of upper left, lower left, upper right and lower rightpartial domains. In addition, the coefficient decoding control unit 123may set a scan order of frequency components in the partial domainhaving a 2×2 size to a scan order of upper left, lower left, upper rightand lower right frequency components.

In addition, the coefficient decoding control unit 123 may employ thescan order illustrated in FIG. 27 (a) in a case where a probability thatnon-zero transform coefficients concentrate in the vertical direction ishigh.

In addition, as illustrated in FIG. 27(b), the coefficient decodingcontrol unit 123 may set a scan order in the partial domain units in asub-block to a scan order of upper left, upper right, lower left andlower right partial domains. Further, the coefficient decoding controlunit 123 may set a scan order of frequency components in the partialdomain having a 2×2 size to a scan order of upper left, upper right,lower left and lower right frequency components.

Furthermore, the coefficient decoding control unit 123 may employ thescan order illustrated in FIG. 27(b) in a case where a probability thatnon-zero transform coefficients concentrate in the horizontal directionis high.

In addition, the above-described scan orders may be stored in the scanorder table storage unit 122.

[Operations and Effects]

As mentioned above, the moving image decoding apparatus 1 related to theModification Example 4 includes an arithmetic decoding device whichdecodes coded data which is obtained by arithmetically coding varioussyntaxes indicating a transform coefficient with respect to eachtransform coefficient which is obtained for each frequency component byperforming frequency transform on a target image for each unit domain.The arithmetic decoding device includes sub-block splitting means forsplitting a target frequency domain corresponding to a process targetunit domain into sub-blocks each having a 4×4 size according to apredetermined definition; and transform coefficient decoding means fordecoding a transform coefficient by using a scan order in a partialdomain with respect to respective partial domains each having a 2×2size, obtained by splitting the sub-block having the 4×4 size into fourdomains.

According to the configuration, since coordinates in a scan order (forexample, coordinates of frequency components adjacent to each other inthe scan order) can be prevented from being considerably changed,transform coefficients which have spatially the same kinds ofcharacteristics as each other can be sequentially decoded. As a result,coding efficiency is improved.

In addition, a change of the context indexes in a scan order in asub-block is minimized.

For example, in a case where the arrangements of values of the contextindexes illustrated in FIGS. 26(a) to 26(d), the number of changes in 0sand 1s of the context indexes in a backward scan order is at most one.

In addition, the present invention is not limited thereto, and isapplicable to arrangements other than the arrangements of values of thecontext indexes illustrated in FIGS. 26(a) to 26(d). For example, in acase where the scan order illustrated in FIG. 27(a) is employed in thearrangement of values of the context indexes of FIG. 52(c), and the scanorder illustrated in FIG. 27(b) is employed in the arrangement of valuesof the context indexes of FIG. 52(b), the number of changes can berestricted to one.

Modification Example 5: Other Patterns

Hereinafter, with reference to FIGS. 28 to 32, a description will bemade of using a context index derivation method having three stages in apredetermined context derivation pattern.

The arrangement of values of context indexes described hitherto is anarrangement using values of two stages. For example, in the arrangementof values of context indexes according to the related art, describedwith reference to FIGS. 51 and 52, values of two stages are taken ineach pattern so that sigCtx=0 or 1 in the patterns 0 to 2, and sigCtx=1or 2 in the pattern 3. By increasing these stages, it is possible torealize an arrangement of values of context indexes which are moresuitable for actual occurrence circumstances of a transform coefficient.

In the present modification example, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c obtains a pattern indexidxCG (patterns 0 to 3) by using the above Equation (A). In addition,the adjacent sub-block coefficient presence/absence context derivingunit 124 c uses a context index derivation method having three stages inthe patterns 0 to 2. Further, context indicating that coding efficiencyis highest at positions of a Y coordinate yB=0 of a sub-block and an Xcoordinate xB=0 of the sub-block is used in the patterns 1 and 2.Hereinafter, specific modification examples will be described.

Modification Example 5-1

With reference to FIGS. 28 and 29, Modification Example 5-1 will bedescribed. FIG. 28 is a diagram illustrating still another example of apseudo-code for deriving a context index from coordinates of a processtarget frequency component in a sub-block according to a pattern indexidxCG obtained from Equation (A). FIG. 29 illustrates arrangements ofvalues of context indexes in the context index derivation method usingthe pseudo-code illustrated in FIG. 28.

With reference to FIGS. 28 and 29, a description will be made of a valueof a context index which is derived in each case of patterns 0 to 3. Inaddition, hatched parts illustrated in FIG. 29 are parts which arechanged from the arrangements of values of context indexes illustratedin FIG. 52.

(Case of Pattern 0)

In a case of the pattern 0, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index asfollows according to a value of xB+yB.

In a case where xB+yB is equal to or smaller than 0, the adjacentsub-block coefficient presence/absence context deriving unit 124 cderives sigCtx=2. In addition, in a case where xB+yB is greater than 0and is equal to or smaller than 2, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives sigCtx=1. In othercases, the adjacent sub-block coefficient presence/absence contextderiving unit 124 c derives sigCtx=0. Consequently, values of contextindexes are arranged as illustrated in FIG. 29 (a).

(Case of Pattern 1)

In a case of the pattern 1, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index asfollows according to a value of yB.

In a case where yB is equal to or smaller than 0, the adjacent sub-blockcoefficient presence/absence context deriving unit 124 c derivessigCtx=2. In addition, in a case where yB is greater than 0 and is equalto or smaller than 1, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives sigCtx=1. In othercases, the adjacent sub-block coefficient presence/absence contextderiving unit 124 c derives sigCtx=0. Consequently, values of contextindexes are arranged as illustrated in FIG. 29 (b).

In other words, as illustrated in FIG. 29(b), values of the contextindexes are 2 in the first row of the sub-block, and values of thecontext indexes are 1 in the second row of the sub-block. In addition,values of the context indexes are 0 in the third row and the fourth rowof the sub-block.

(Case of Pattern 2)

In a case of the pattern 2, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index asfollows according to a value of xB.

In a case where xB is equal to or smaller than 0, the adjacent sub-blockcoefficient presence/absence context deriving unit 124 c derivessigCtx=2. In addition, in a case where xB is greater than 0 and is equalto or smaller than 1, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives sigCtx=1. In othercases, the adjacent sub-block coefficient presence/absence contextderiving unit 124 c derives sigCtx=0. Consequently, values of contextindexes are arranged as illustrated in FIG. 29 (c).

In other words, as illustrated in FIG. 29(c), values of the contextindexes are 2 in the first column of the sub-block, and values of thecontext indexes are 1 in the second column of the sub-block. Inaddition, values of the context indexes are 0 in the third column andthe fourth column of the sub-block.

(Case of Pattern 3)

In a case of the pattern 3, as illustrated in FIG. 29(d), the adjacentsub-block coefficient presence/absence context deriving unit 124 cequally derives sigCtx=2 in the sub-block regardless of values of xB andyB.

In addition, the arrangements of context indexes related to a case ofModification Example 5-1 may be realized by using a pseudo-codeillustrated in FIG. 56. FIG. 56 is an example of another pseudo-code forrealizing the arrangements of the values of the context indexesillustrated in FIG. 29. More specifically, the pseudo-code illustratedin FIG. 56 is one in which a boundary value for magnitude relationdetermination is changed, or the magnitude relation determination ischanged to equal value determination, in the pseudo-code illustrated inFIG. 29. According to the pseudo-code illustrated in FIG. 56, it ispossible to realize the arrangements of values of the context indexesillustrated in FIG. 29 in the same manner as the pseudo-code illustratedin FIG. 29.

General Configuration of Modification Example 5

With reference to FIG. 30, a description will be made of a generalconfiguration of a pseudo-code for deriving a context index ofModification Example 5. In the general configuration, a context index isderived by using predetermined threshold values TH1, TH2, TH3, TH4, andTH5.

(Case of Pattern 0)

In a case of the pattern 0, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index asfollows according to a value of xB+yB.

In a case where xB+yB is equal to or smaller than TH1, the adjacentsub-block coefficient presence/absence context deriving unit 124 cderives sigCtx=2. In addition, in a case where xB+yB is greater than TH1and is equal to or smaller than TH2, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives sigCtx=1. In othercases, the adjacent sub-block coefficient presence/absence contextderiving unit 124 c derives sigCtx=0.

(Case of Pattern 1)

In a case of the pattern 1, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index asfollows according to a value of yB.

In a case where yB is equal to or smaller than TH3, the adjacentsub-block coefficient presence/absence context deriving unit 124 cderives sigCtx=2. In addition, in a case where yB is greater than TH3and is equal to or smaller than TH4, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives sigCtx=1. In othercases, the adjacent sub-block coefficient presence/absence contextderiving unit 124 c derives sigCtx=0. Consequently, values of contextindexes are arranged as illustrated in FIG. 31(b).

In other words, values of the context indexes are 2 in the (TH3-1)-thand subsequent rows of the sub-block, and values of the context indexesare 1 from the TH3-th row to the (TH4-1)-th row. In addition, values ofthe context indexes are 0 in the TH4-th row of the sub-block.

(Case of Pattern 2)

In a case of the pattern 2, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index asfollows according to a value of xB.

In a case where xB is equal to or smaller than TH3, the adjacentsub-block coefficient presence/absence context deriving unit 124 cderives sigCtx=2. In addition, in a case where xB is greater than TH3and is equal to or smaller than TH4, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives sigCtx=1. In othercases, the adjacent sub-block coefficient presence/absence contextderiving unit 124 c derives sigCtx=0.

In other words, values of the context indexes are 2 in the (TH3-1)-thand subsequent columns of the sub-block, and values of the contextindexes are 1 from the TH3-th column to the (TH4-1)-th column. Inaddition, values of the context indexes are 0 in the TH4-th column ofthe sub-block.

(Case of Pattern 3)

In a case of the pattern 3, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index byusing sigCtx=(xB+yB<=TH5) ? 2:1.

Therefore, in a case of the pattern 3, if a sum of the coordinate xB inthe horizontal direction of the coordinates (xB,yB) in the sub-block andthe coordinate yB in the vertical direction is equal to or smaller thanTH5, a value of a context index is “2”, and, otherwise, a value of acontext index is “1”.

Modification Example 5-1 described above is an example of TH1=0, TH2=2,TH3=0, TH4=1, and TH5=6. From the test performed by the presentinventor, it has been confirmed that Modification Example 5-1 canfurther improve coding efficiency than the comparative example of FIGS.51 and 52, especially, in an intra-prediction block. In relation to theelements of Modification Example 5-1, in the pattern 0, a value of acontext index at the upper left position is set to 2 which indicates anoccurrence probability is high; in the pattern 1 and the pattern 2,values of context indexes at the first row and the first column are setto 2 which indicates an occurrence probability is high; and, in thepattern 3, a value of a context index is set to a fixed value (here, 2which indicates an occurrence probability is high). It has beenconfirmed from the test performed by the present inventor that codingefficiency is considerably improved by changing the patterns 1 and 2,coding efficiency is improved in an intermediate extent by changing thepattern 0, and coding efficiency is not reduced in the simplificationsuch as changing of the pattern 3.

In addition, in the pattern 0, it is appropriate that TH1 is equal to orgreater than 0, and TH2 is smaller than 6 in terms of coding efficiency.In the patterns 1 and 2, it is appropriate that TH3 is equal to orgreater than 0, and TH4 is smaller than 6 in terms of coding efficiency.In the pattern 3, it is appropriate that TH5 is equal to or greater than6.

Hereinafter, with reference to FIGS. 31 to 33, and FIG. 53, adescription will be further made of Modification Example 5-2,Modification Example 5-3, Modification Example 5-4, and ModificationExample 5-5.

Modification Example 5-2

With reference to FIG. 31, Modification Example 5-2 will be described.Modification Example 5-2 is an example of TH1=−1, TH2=2, TH3=0, TH4=1,and TH5=6. In relation of elements of Modification Example 5-2, inpatterns 1 and 2, values of context indexes of the first row and thefirst column are set to 2, and, in a pattern 3, a value of a contextindex is set to a fixed value (here, 2).

FIG. 31 illustrates arrangements of values of context indexes in acontext index derivation method of Modification Example 5-2. Withreference to FIG. 31, a description will be made of a value of a contextindex which is derived in each case of the patterns 0 to 3. In addition,hatched parts illustrated in FIG. 31 are parts which are changed fromthe arrangements of values of context indexes illustrated in FIG. 52.

(Case of Pattern 0)

As illustrated in FIG. 31(a), there are the same derivation method andan arrangement of the same values as in the comparative example of FIGS.51 and 52.

(Case of Patterns 1 to 3)

As illustrated in FIGS. 31(b) to 31(c), there are the same derivationmethod and an arrangement of the same values as in Modification Example5-1 of FIGS. 28 and 29.

In addition, the arrangements of context indexes related to a case ofModification Example 5-2 may be realized by using a pseudo-codeillustrated in FIG. 57. FIG. 57 is an example of another pseudo-code forrealizing the arrangements of the values of the context indexesillustrated in FIG. 31.

More specifically, the pseudo-code illustrated in FIG. 57 is one inwhich a boundary value for magnitude relation determination is changed,or the magnitude relation determination is changed to equal valuedetermination, as appropriate, in the pseudo-code of FIG. 30 includingTH1=−1, TH2=2, TH3=0, TH4=1, and TH5=6, in order to realize thearrangements of the values of the context indexes illustrated in FIG.31.

According to the pseudo-code illustrated in FIG. 57, it is possible torealize the arrangements of values of the context indexes illustrated inFIG. 31 in the same manner as in a case where threshold values are setto TH1=−1, TH2=2, TH3=0, TH4=1, and TH5=6 in the pseudo-code illustratedin FIG. 30.

As described above, the context index derivation method of ModificationExample 5-2 can achieve effects of improvement of coding efficiency bysetting values of the context indexes of the first row and the firstcolumn to 2 in the patterns 1 and 2, and simplification by setting avalue of the context index to a fixed value in the pattern 3, in thesame manner as Modification Example 5-1. In addition, unlikeModification Example 5-1, values of context indexes of the pattern 0 areonly 0 and 1 of two stages, and thus complexity of Modification Example5-2 is lower than that of Modification Example 5-1. From the testperformed by the present inventor, it has been confirmed that, in thesame manner as Modification Example 5-1, Modification Example 5-2 canalso improve coding efficiency than the comparative example of FIGS. 51and 52, especially, in an intra-prediction block.

Modification Example 5-3

With reference to FIG. 32, Modification Example 5-3 will be described.Modification Example 5-3 is an example of TH1=−1, TH2=2, TH3=0, TH4=2,and TH5=4. In relation of elements of Modification Example 5-2, inpatterns 1 and 2, values of context indexes of the first row and thefirst column are set to 2, and, in patterns 1 and 2, values of contextindexes of the third row and the third column are set to 1.

FIG. 32 illustrates arrangements of values of context indexes in acontext index derivation method of Modification Example 5-3. Withreference to FIG. 32, a description will be made of a value of a contextindex which is derived in each case of the patterns 0 to 3. In addition,hatched parts illustrated in FIG. 32 are parts which are changed fromthe arrangements of values of context indexes illustrated in FIG. 52.

(Case of Pattern 0)

As illustrated in FIG. 32(a), there are the same derivation method andan arrangement of the same values as in the comparative example of FIGS.51 and 52.

(Case of Pattern 1)

In a case of the pattern 1, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index asfollows according to a value of yB.

In a case where yB is equal to or smaller than 0, the adjacent sub-blockcoefficient presence/absence context deriving unit 124 c derivessigCtx=2. In addition, in a case where yB is greater than 0 and is equalto or smaller than 2, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives sigCtx=1. In othercases, the adjacent sub-block coefficient presence/absence contextderiving unit 124 c derives sigCtx=0. Consequently, values of contextindexes are arranged as illustrated in FIG. 32(b).

In other words, as illustrated in FIG. 32(b), values of the contextindexes are 2 in the first row of the sub-block, and values of thecontext indexes are 1 in the second and third rows of the sub-block. Inaddition, values of the context indexes are 0 in the fourth row of thesub-block.

(Case of Pattern 2)

In a case of the pattern 3, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index asfollows according to a value of xB.

In a case where xB is equal to or smaller than 0, the adjacent sub-blockcoefficient presence/absence context deriving unit 124 c derivessigCtx=2. In addition, in a case where xB is greater than 0 and is equalto or smaller than 2, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives sigCtx=1. In othercases, the adjacent sub-block coefficient presence/absence contextderiving unit 124 c derives sigCtx=0. Consequently, values of contextindexes are arranged as illustrated in FIG. 32(c).

In other words, as illustrated in FIG. 32(c), values of the contextindexes are 2 in the first column of the sub-block, and values of thecontext indexes are 1 in the second and third columns of the sub-block.In addition, values of the context indexes are 0 in the fourth column ofthe sub-block.

(Case of Pattern 3)

As illustrated in FIG. 32(d), there are the same derivation method andan arrangement of the same values as in the comparative example of FIGS.51 and 52.

In addition, the arrangements of context indexes related to a case ofModification Example 5-3 may be realized by using a pseudo-codeillustrated in FIG. 58. FIG. 58 is an example of another pseudo-code forrealizing the arrangements of the values of the context indexesillustrated in FIG. 32.

More specifically, the pseudo-code illustrated in FIG. 58 is one inwhich a boundary value for magnitude relation determination is changed,or the magnitude relation determination is changed to equal valuedetermination, as appropriate, in the pseudo-code of FIG. 32 includingTH1=−1, TH2=2, TH3=0, TH4=1, and TH5=4, in order to realize thearrangements of the values of the context indexes illustrated in FIG.32.

According to the pseudo-code illustrated in FIG. 58, it is possible torealize the arrangements of values of the context indexes illustrated inFIG. 32 in the same manner as in a case where threshold values are setto TH1=−1, TH2=2, TH3=0, TH4=1, and TH5=4 in the pseudo-code illustratedin FIG. 30.

As described above, the context index derivation method of ModificationExample 5-3 can improve coding efficiency by setting values of thecontext indexes of the first row and the first column to 2 in thepatterns 1 and 2 in the same manner as in Modification Example 5-1.

Modification Example 5-4

With reference to FIG. 33, Modification Example 5-4 will be described.Modification Example 5-4 is an example of TH1=1, TH2=3, TH3=0, TH4=2,and TH5=6. In relation of elements of Modification Example 5-4, inpatterns 1 and 2, values of context indexes of the first row and thefirst column are set to 2, and, in patterns 1 and 2, values of contextindexes of the third row and the third column are set to 1.

FIG. 33 illustrates arrangements of values of context indexes in acontext index derivation method of Modification Example 5-4. Withreference to FIG. 33, a description will be made of a value of a contextindex which is derived in each case of the patterns 0 to 3. In addition,hatched parts illustrated in FIG. 33 are parts which are changed fromthe arrangements of values of context indexes illustrated in FIG. 52.

(Case of Pattern 0)

In a case of the pattern 0, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index asfollows according to a value of xB+yB.

In a case where xB+yB is equal to or smaller than 1, the adjacentsub-block coefficient presence/absence context deriving unit 124 cderives sigCtx=2. In addition, in a case where xB+yB is greater than 1and is equal to or smaller than 3, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives sigCtx=1. In othercases, the adjacent sub-block coefficient presence/absence contextderiving unit 124 c derives sigCtx=0. Consequently, values of contextindexes are arranged as illustrated in FIG. 33(a).

(Case of Patterns 1 and 2)

As illustrated in FIGS. 33(b) and 33(c), there are the same derivationmethod and an arrangement of the same values as in Modification Example5-3 of FIG. 32.

(Case of Pattern 3)

As illustrated in FIG. 33(d), there are the same derivation method andan arrangement of the same values as in the Modification Example 5-1 ofFIGS. 28 and 29.

In addition, the arrangements of context indexes related to a case ofModification Example 5-4 may be realized by using a pseudo-codeillustrated in FIG. 59. FIG. 59 is an example of another pseudo-code forrealizing the arrangements of the values of the context indexesillustrated in FIG. 33.

More specifically, the pseudo-code illustrated in FIG. 59 is one inwhich a boundary value for magnitude relation determination is changed,or the magnitude relation determination is changed to equal valuedetermination, as appropriate, in the pseudo-code of FIG. 30 includingTH1=1, TH2=3, TH3=0, TH4=2, and TH5=6, in order to realize thearrangements of the values of the context indexes illustrated in FIG.33.

According to the pseudo-code illustrated in FIG. 57, it is possible torealize the arrangements of values of the context indexes illustrated inFIG. 33 in the same manner as in a case where threshold values are setto TH1=−1, TH2=2, TH3=0, TH4=1, and TH5=6 in the pseudo-code illustratedin FIG. 30.

As described above, the context index derivation method of ModificationExample 5-4 can improve coding efficiency by setting values of thecontext indexes of the first row and the first column to 2 in thepatterns 1 and 2 in the same manner as in Modification Example 5-3. Inaddition, in the same manner as in Modification Example 5-1, it ispossible to improve coding efficiency by using 0, 1, 2, and 3 of threestages as values of context indexes in the pattern 0. Further, in thesame manner as in Modification Example 5-1, it is possible to achieve aneffect of simplification by setting a value of a context index to afixed value in the pattern 3.

Modification Example 5-5

With reference to FIG. 53, Modification Example 5-5 will be described.Modification Example 5-5 is an example of TH1=−1, TH2=2, TH3=−1, TH4=1,and TH5=6. In relation of elements of Modification Example 5-5, in apattern 3, a value of a context index is set to a fixed value (here, 2).FIG. 53 illustrates arrangements of values of context indexes in acontext index derivation method of Modification Example 5-5. Withreference to FIG. 53, a description will be made of a value of a contextindex which is derived in each case of the patterns 0 to 3. In addition,hatched parts illustrated in FIG. 53 are parts which are changed fromthe arrangements of values of context indexes illustrated in FIG. 52.

(Case of Patterns 0 to 2)

As illustrated in FIGS. 53(a) to 53(c), there are the same derivationmethod and an arrangement of the same values as in the comparativeexample of FIGS. 51 and 52.

(Case of Pattern 3)

As illustrated in FIG. 53(d), there are the same derivation method andan arrangement of the same values as in Modification Example 5-1 ofFIGS. 28 and 29.

In addition, the arrangements of context indexes related to a case ofModification Example 5-5 may be realized by using a pseudo-codeillustrated in FIG. 60. FIG. 60 is an example of another pseudo-code forrealizing the arrangements of the values of the context indexesillustrated in FIG. 53.

More specifically, the pseudo-code illustrated in FIG. 60 is one inwhich a boundary value for magnitude relation determination is changed,or the magnitude relation determination is changed to equal valuedetermination, as appropriate, in the pseudo-code of FIG. 30 includingTH1=−1, TH2=2, TH3=−1, TH4=1, and TH5=6, in order to realize thearrangements of the values of the context indexes illustrated in FIG.53.

According to the pseudo-code illustrated in FIG. 60, it is possible torealize the arrangements of values of the context indexes illustrated inFIG. 53 in the same manner as in a case where threshold values are setto TH1=−1, TH2=2, TH3=−1, TH4=1, and TH5=6, in the pseudo-codeillustrated in FIG. 30.

Modification Example 5-6

With reference to FIG. 61, Modification Example 5-6 will be described.Modification Example 5-6 is an example of TH1=1, TH2=2, TH3=0, TH4=1,and TH5=6. In relation of elements of Modification Example 5-6, in apattern 0, a value of a context index indicating that an occurrenceprobability of a non-zero transform coefficient is high is set to a partsatisfying xB+yB<2.

FIG. 61 illustrates arrangements of values of context indexes in acontext index derivation method of Modification Example 5-6. Withreference to FIG. 61, a description will be made of a value of a contextindex which is derived in each case of the patterns 0 to 3.

(Case of Pattern 0)

In a case of the pattern 0, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index asfollows according to a value of xB+yB.

In a case where xB+yB is equal to or smaller than 1, the adjacentsub-block coefficient presence/absence context deriving unit 124 cderives sigCtx=2. In addition, in a case where xB+yB is greater than 1and is equal to or smaller than 2, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives sigCtx=1. In othercases, the adjacent sub-block coefficient presence/absence contextderiving unit 124 c derives sigCtx=0. Consequently, values of contextindexes are arranged as illustrated in FIG. 61(a).

(Case of Patterns 1 to 3)

FIGS. 61(b) to 61(d) illustrate the same derivation method andarrangements of the same values as in the Modification Example 5-1 ofFIGS. 29(b), 29(c) and 29(d).

In addition, the arrangements of context indexes related to a case ofModification Example 5-6 may be realized by using a pseudo-codeillustrated in FIG. 62. The pseudo-code illustrated in FIG. 62 may beobtained by changing a boundary value for magnitude relationdetermination, or by changing the magnitude relation determination toequal value determination, in the pseudo-code illustrated in FIG. 30, asdescribed in the above-described modification example.

As described above, the context index derivation method of ModificationExample 5-6 can achieve effects of improvement of coding efficiency bysetting values of the context indexes of the first row and the firstcolumn to 2 in the patterns 1 and 2, and simplification by setting avalue of the context index to a fixed value in the pattern 3, in thesame manner as Modification Example 5-1. Particularly, in a case wherecontext indexes are derived from an 8×8 TU to a 32×32 TU by the adjacentsub-block coefficient presence/absence context deriving unit 124 c, itis possible to achieve an effect of improvement of coding efficiency bysetting a value of a context index indicating that an occurrenceprobability of a non-zero transform coefficient is high to a partsatisfying xB+yB<2 in the pattern 0.

Modification Example 5-7

With reference to FIG. 63, Modification Example 5-7 will be described.Modification Example 5-7 is an example of TH1=1, TH2=3, TH3=0, TH4=1,and TH5=6. In relation of elements of Modification Example 5-7, in apattern 0, a value of a context index indicating that an occurrenceprobability of a non-zero transform coefficient is high is set to a partsatisfying xB+yB<2, and a value of a context index indicating that anoccurrence probability of a non-zero transform coefficient isintermediate is set to a part satisfying 1<xB+yB<4.

FIG. 63 illustrates arrangements of values of context indexes in acontext index derivation method of Modification Example 5-7. Withreference to FIG. 63, a description will be made of a value of a contextindex which is derived in each case of the patterns 0 to 3.

(Case of Pattern 0)

FIG. 63(a) illustrates the same derivation method and arrangements ofthe same values as in the Modification Example 5-4 of FIG. 33(a).

(Case of Patterns 1 to 3)

FIGS. 63(b) to 63(d) illustrate the same derivation method andarrangements of the same values as in the Modification Example 5-1 ofFIGS. 29(b), 29(c) and 29(d).

In addition, the arrangements of context indexes related to a case ofModification Example 5-7 may be realized by using a pseudo-codeillustrated in FIG. 64. The pseudo-code illustrated in FIG. 64 may beobtained by changing a boundary value for magnitude relationdetermination, or by changing the magnitude relation determination toequal value determination, in the pseudo-code illustrated in FIG. 30, asdescribed in the above-described modification example.

As described above, the context index derivation method of ModificationExample 5-7 can achieve effects of improvement of coding efficiency bysetting values of the context indexes of the first row and the firstcolumn to a value of a context index indicating that an occurrenceprobability of a non-zero transform coefficient is high in the patterns1 and 2, and simplification by setting a value of the context index to afixed value in the pattern 3, in the same manner as Modification Example5-1. Particularly, in a case where context indexes are derived from an8×8 TU to a 32×32 TU by the adjacent sub-block coefficientpresence/absence context deriving unit 124 c, it is possible to achievean effect of improvement of coding efficiency by setting a value of acontext index indicating that an occurrence probability of a non-zerotransform coefficient is high to a part satisfying xB+yB<2, and bysetting a value of a context index indicating that an occurrenceprobability of a non-zero transform coefficient is intermediate to apart satisfying 1<xB+yB<4 in the pattern 0.

Supplements Related to Modification Example 5

In addition, in the moving image decoding apparatus 1 related toModification Examples 5-1, 5-4, 5-6 and 5-7 described above, the contextindex deriving means determines a sub-block coefficient presence/absenceflag for a right adjacent sub-block which is a sub-block adjacent to theright side of a process target sub-block and a lower adjacent sub-blockwhich is adjacent to the lower side thereof. When it is determined thata non-zero transform coefficient is not present in either the rightadjacent sub-block or the lower adjacent sub-block, on the basis of thedetermination result, the context index deriving means derives thecontext index corresponding to a case where an occurrence probability ofa non-zero transform coefficient is high in a case where a sum of xB andyB indicating a coefficient position in a sub-block is equal to orsmaller than a first threshold value; derives the context indexcorresponding to a case where an occurrence probability of a non-zerotransform coefficient is intermediate in a case where the sum of xB andyB is greater than the first threshold value and is equal to or smallerthan a second threshold value; and derives the context indexcorresponding to a case where an occurrence probability of a non-zerotransform coefficient is low in a case where the sum of xB and yB isgreater than the second threshold value.

According to the configuration, it is possible to realize a contextderivation pattern which is more suitable for an actual occurrenceprobability of a transform coefficient, and thus it is possible toimprove coding efficiency.

Particularly, by setting the first threshold value to 0 and the secondthreshold value to 2, it is possible to realize a preferable contextderivation pattern which is more suitable for an actual occurrenceprobability of a non-zero transform coefficient. In addition,preferably, the first threshold value may be set to 1, and the secondthreshold value may be set to 2. Further, preferably, the firstthreshold value may be set to 1, and the second threshold value may beset to 3.

In addition, in the moving image decoding apparatus 1 related toModification Examples 5-1 to 5-4, 5-6 and 5-7 described above, thecontext index deriving means determines a sub-block coefficientpresence/absence flag for a right adjacent sub-block which is asub-block adjacent to the right side of a process target sub-block and alower adjacent sub-block which is adjacent to the lower side thereof.When it is determined that a non-zero transform coefficient is notpresent in one of the right adjacent sub-block and the lower adjacentsub-block, the context index deriving means selects a coefficientposition of one of xB and yB indicating a coefficient position in asub-block in an adjacent direction of a sub-block in which it isdetermined that a non-zero transform coefficient is not present; derivesthe context index corresponding to a case where an occurrenceprobability of a non-zero transform coefficient is high in a case wherethe coefficient position is equal to or smaller than a first thresholdvalue; derives the context index corresponding to a case where anoccurrence probability of a non-zero transform coefficient isintermediate in a case where the coefficient position is greater thanthe first threshold value and is equal to or smaller than a secondthreshold value; and derives the context index corresponding to a casewhere an occurrence probability of a non-zero transform coefficient islow in a case where the coefficient position is greater than the secondthreshold value.

According to the configuration, it is possible to set a preferablethreshold value to an actual occurrence probability of a transformcoefficient and thus to realize a more suitable context derivationpattern. Therefore, it is possible to improve coding efficiency.

In addition, in the moving image decoding apparatus 1 related toModification Examples 5-1, 5-3, 5-4 and 5-5 described above, the contextindex deriving means determines a sub-block coefficient presence/absenceflag for a right adjacent sub-block which is a sub-block adjacent to theright side of a process target sub-block and a lower adjacent sub-blockwhich is adjacent to the lower side thereof. When it is determined thata non-zero transform coefficient is present in both the right adjacentsub-block and the lower adjacent sub-block with respect to a processtarget sub-block, the context index deriving means derives a fixedcontext index with respect to a non-zero transform coefficient in theprocess target sub-block.

According to the configuration, it is possible to minimize a reductionin coding efficiency and also to simplify derivation of a context index.

In addition, in the configuration, the fixed context index is preferablya context index corresponding to a case where an occurrence frequency ofa non-zero transform coefficient is high.

According to the configuration, it is possible to fixedly derive acontext index which is more suitable for an actual occurrenceprobability of a transform coefficient and corresponds to a case wherean occurrence probability of a non-zero transform coefficient is high.Therefore, since a fixed context index which is more suitable for anactual occurrence probability of a transform coefficient can be derived,it is possible to further minimize a reduction in coding efficiency andalso to simplify derivation of a context index.

[Operations and Effects]

As described above, the moving image decoding apparatus 1 related toModification Examples 5-1 to 5-4, 5-6 and 5-7 includes an arithmeticdecoding device which decodes coded data which is obtained byarithmetically coding various syntaxes indicating a transformcoefficient with respect to each transform coefficient which is obtainedfor each frequency component by performing frequency transform on atarget image for each unit domain. The arithmetic decoding deviceincludes sub-block splitting means for splitting a target frequencydomain corresponding to a process target unit domain into sub-blockseach having a predetermined size; sub-block coefficient presence/absenceflag decoding means for decoding a sub-block coefficientpresence/absence flag indicating whether or not at least one non-zerotransform coefficient is included in the sub-block with respect to therespective sub-blocks into which the frequency domain is split by thesub-block splitting means; non-zero transform coefficient determiningmeans for determining whether or not at least one non-zero transformcoefficient is included in a sub-block adjacent to a process targetsub-block on the basis of the decoded sub-block coefficientpresence/absence flag; and context index deriving means for deriving acontext index assigned to a transform coefficient presence/absence flagwhich is syntax indicating whether or not the transform coefficient is0, in which, when a non-zero transform coefficient is not present in anyof sub-blocks adjacent to the process target sub-block, on the basis ofthe determination result, the context index deriving means derives thecontext indexes which respectively correspond to a case where anoccurrence probability of a non-zero transform coefficient is low, acase where an occurrence probability of a non-zero transform coefficientis high, and a case where an occurrence probability of a non-zerotransform coefficient is intermediate between the high case and the lowcase, according to a position of a process target transform coefficientin the process target sub-block.

In the moving image decoding apparatus 1 related to ModificationExamples 5-1, 5-4, 5-6 and 5-7 described above, when it is determinedthat a non-zero transform coefficient is not present in any of two ormore sub-blocks adjacent to the process target sub-block, on the basisof the determination result, the context index deriving means derivesthe context indexes which respectively correspond to a case where anoccurrence probability of a non-zero transform coefficient is low, acase where an occurrence probability of a non-zero transform coefficientis high, and a case where an occurrence probability of a non-zerotransform coefficient is intermediate between the high case and the lowcase, according to a position of a process target transform coefficientin the process target sub-block. Therefore, it is possible to improvecoding efficiency. Particularly, a case where an occurrence probabilityof a non-zero transform coefficient is high is preferably assigned to anupper left position in the process target sub-block.

In the moving image decoding apparatus 1 related to ModificationExamples 5-1 to 5-4, 5-6 and 5-7 described above, when it is determinedthat a non-zero transform coefficient is present in one or moresub-blocks adjacent to the process target sub-block and is not presentin one or more sub-blocks, on the basis of the determination result, thecontext index deriving means derives the context indexes whichrespectively correspond to a case where an occurrence probability of anon-zero transform coefficient is low, a case where an occurrenceprobability of a non-zero transform coefficient is high, and a casewhere an occurrence probability of a non-zero transform coefficient isintermediate between the high case and the low case, according to aposition of a process target non-zero transform coefficient in theprocess target sub-block. Therefore, it is possible to improve codingefficiency. Particularly, in a sub-block of which a non-zero transformcoefficient is determined as being present in a sub-block adjacent tothe right side and a non-zero transform coefficient is determined asbeing present in a sub-block adjacent to the lower side, a case where anoccurrence probability of a non-zero transform coefficient is high ispreferably assigned to a first row in the process target sub-block.Symmetrically thereto, particularly, in a sub-block of which a non-zerotransform coefficient is determined as being present in a sub-blockadjacent to the lower side and a non-zero transform coefficient isdetermined as being present in a sub-block adjacent to the right side, acase where an occurrence probability of a non-zero transform coefficientis high is preferably assigned to a first column in the process targetsub-block.

In the moving image decoding apparatus 1 related to ModificationExamples 5-1, 5-3, 5-4, 5-5, 5-6 and 5-7 described above, when it isdetermined that a non-zero transform coefficient is present in two ormore sub-blocks adjacent to the process target sub-block, on the basisof the determination result, the context index deriving means fixedlyderives the context index corresponding to a case where an occurrenceprobability of a non-zero transform coefficient is high, and cansimplify derivation of the context index.

According to the configuration related to Modification Examples 5-1 to5-4, 5-6 and 5-7 described above, it is possible to realize a contextderivation pattern which is more suitable for an actual occurrenceprobability of a transform coefficient, and thus it is possible toimprove coding efficiency.

Combination Between Modification Example 5 and Modification Example 1

In addition, Modification Example 5 may be combined with ModificationExample 1. Modification Example 5 is a configuration in which aseparation of a stage for a value of a context index is set in thefollowing condition as described above. In other words, in the pattern0, a separation of a stage for a value of a context index is setaccording to xB+yB. In the pattern 1, a separation of a stage for avalue of a context index is set according to yB. In the pattern 2, aseparation of a stage for a value of a context index is set according toxB. Further, in the pattern 3, a separation of a stage for a value of acontext index is set according to xB+yB, or a value of a context indexcorresponding to a case where an occurrence probability of a non-zerotransform coefficient is high is equally set.

In a decoding process of a transform coefficient using the scan order ofModification Example 1, a context index is derived according to thecondition related to Modification Example 5, and thus the number ofchanges in 0s and 1s of context indexes in a backward scan order in asub-block can be minimized.

More specifically, the following scan order may be used in the patterns0 to 3 of Modification Examples 5-1 to 5-5.

In a case of the pattern 0, as illustrated in FIG. 22 (a), thecoefficient decoding control unit 123 may apply the up-right diagonalscan thereto.

In a case of the pattern 1, as illustrated in FIG. 22(b), thecoefficient decoding control unit 123 applies the horizontal fast scanthereto. In other words, in a case of(significant_coeff_group_flag[xCG+1][yCG],significant_coeff_group_flag[xCG][yCG+1])=(1,0),the coefficient decoding control unit 123 may apply the horizontal fastscan thereto.

In a case of the pattern 2, as illustrated in FIG. 22 (c), thecoefficient decoding control unit 123 applies the vertical fast scan. Inother words, in a case of(significant_coeff_group_flag[xCG+1][yCG],significant_coeff_group_flag[xCG][yCG+1])=(0,1),the coefficient decoding control unit 123 may apply the vertical fastscan thereto.

In a case of the pattern 3, as illustrated in FIG. 22 (d), thecoefficient decoding control unit 123 may apply the up-right diagonalscan.

Modification Example 6: Reference to Absolute Coordinate

Hereinafter, with reference to FIGS. 34 and 35, a description will bemade of a modification example of deriving a context index by using notonly coordinates (xB,yB) in a sub-block but also a coefficient position(xC,yC) in a TU.

In the present modification example, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c obtains a pattern indexidxCG by using the above Equation (A), and also derives a context indexin a method illustrated in FIG. 34 according to patterns 0 to 3 obtainedtherefrom.

FIG. 34 is a diagram illustrating still another example of a pseudo-codefor deriving a context index from coordinates of a process targetfrequency component in a sub-block according to a pattern index idxCGobtained from Equation (A). FIG. 35 illustrates arrangements of valuesof context indexes in the context index derivation method using thepseudo-code illustrated in FIG. 34.

With reference to FIGS. 34 and 35, a description will be made of a valueof a context index which is derived in each case of patterns 0 to 3.

(Case of Pattern 0)

In a case of the pattern 0, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index byusing sigCtx=(xB+yB<=2)<=0) ? 1:0.

In other words, a case of the pattern 0 is the same as a case of thepattern 0 of the above Example. Therefore, values of the context indexesare arranged as illustrated in FIG. 35(a).

(Case of Pattern 1)

In a case of the pattern 1, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context indexaccording to the Y coordinate yC of the coefficient position (xC,yC).

In a case where yC is 0, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives sigCx=2. Therefore,values the context indexes are arranged as illustrated in FIG. 35(e). Inother words, in a case where yC is 0, as illustrated in FIG. 35(e),values of the context indexes are 2 in the first row (upper end) of thesub-block.

In contrast, in a case where yC is not 0, the adjacent sub-blockcoefficient presence/absence context deriving unit 124 c derives acontext index by using sigCtx=(yB<=1) ? 1:0.

Consequently, as illustrated in FIG. 35(b), values of the contextindexes are 1 in the first and second rows of the sub-block, and valuesof the context indexes are 0 in the third and fourth rows of thesub-block.

(Case of Pattern 2)

In a case of the pattern 2, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context indexaccording to the Y coordinate xC of the coefficient position (xC,yC).

In a case where xC is 0, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives sigCx=2. Therefore,values the context indexes are arranged as illustrated in FIG. 35(f). Inother words, in a case where yC is 0, as illustrated in FIG. 35(f),values of the context indexes are 2 in the first column (left end) ofthe sub-block.

In contrast, in a case where xC is not 0, the adjacent sub-blockcoefficient presence/absence context deriving unit 124 c derives acontext index by using sigCtx=(xB<=1) ? 1:0.

Consequently, as illustrated in FIG. 35(c), values of the contextindexes are 1 in the first and second columns of the sub-block, andvalues of the context indexes are 0 in the third and fourth columns ofthe sub-block.

(Case of Pattern 3)

In a case of the pattern 3, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index byusing sigCtx=(xB+yB<=4)<=0) ? 1:0.

Therefore, in a case of the pattern 3, if a sum of the coordinate xB inthe horizontal direction of the coordinates (xB,yB) in the sub-block andthe coordinate yB in the vertical direction is equal to or smaller than4, a value of a context index is “1”, and, otherwise, a value of acontext index is “0”.

Consequently, values of the context indexes are arranged as illustratedin FIG. 35(d).

[Operations and Effects]

As mentioned above, the moving image decoding apparatus 1 related toModification Example 6 includes an arithmetic decoding device whichdecodes coded data which is obtained by arithmetically coding varioussyntaxes indicating a transform coefficient with respect to eachtransform coefficient which is obtained for each frequency component byperforming frequency transform on a target image for each unit domain.The arithmetic decoding device includes sub-block splitting means forsplitting a target frequency domain corresponding to a process targetunit domain into sub-blocks each having a predetermined size; sub-blockcoefficient presence/absence flag decoding means for decoding asub-block coefficient presence/absence flag indicating whether or not atleast one non-zero transform coefficient is included in the sub-blockwith respect to the respective sub-blocks into which the frequencydomain is split by the sub-block splitting means; directivitydetermining means for determining a directivity of a distribution oftransform coefficients on the basis of a sub-block coefficientpresence/absence flag in a sub-block adjacent to a process targetsub-block; and context index deriving means for deriving a context indexassigned to a transform coefficient presence/absence flag which issyntax indicating whether or not the transform coefficient is 0, inwhich the context index deriving means derives the context index byusing coordinates in the process target unit domain in the processtarget sub-block according to a directivity determined by thedirectivity determining means.

According to the configuration, in a case of xC=0 or yC=0, a contextindex corresponding to a case where an occurrence probability of anon-zero transform coefficient is high is used in the patterns 1 and 2.

In a case where a horizontal edge or a vertical edge is present,non-zero transform coefficients tend to concentrate and appear in adomain of xC=0 or yC=0.

According to the configuration, since a context index corresponding to acase where an occurrence probability of a non-zero transform coefficientis high is used in a case where a probability of the presence of thehorizontal edge or the vertical edge is high, it is possible to improvecoding efficiency.

Further, in the pattern 1 (pattern 2), in addition to the determinationof yC=0 (xC=0), or instead of the determination, it may be determinedwhether or not xC is 0 and yC is 0, and a context index may be derivedaccording to a determination result.

Modification Example 7: Equally High Probability Pattern

Hereinafter, with reference to FIGS. 36 to 38, a description will bemade of a modification example of equally using a context index in aprocess target sub-block in a case where a probability that there are alarge number of non-zero transform coefficients in an adjacent sub-blockis high.

In a case where a probability that there are a large number of non-zerotransform coefficients in an adjacent sub-block is high, there may be anoccurrence of circumstances in which a large number of non-zerotransform coefficients are equally present in a process targetsub-block.

With reference to FIG. 36, a description will be made of a case ofcircumstances in which a large number of non-zero transform coefficientsare equally present in a process target sub-block regardless ofcoordinates in the sub-block.

In a case where non-zero transform coefficients are present in all of aright adjacent sub-block A, a lower adjacent sub-block B, and a lowerright adjacent sub-block C with respect to a process target sub-block Xillustrated in FIG. 36, there is a tendency for an occurrenceprobability of a non-zero transform coefficient in the sub-block X to beequally high regardless of coordinates in the sub-block X.

In such a case, it is preferable that the context index 1 indicating anoccurrence probability with an intermediate level be not used but thecontext index 2 indicating an occurrence probability with a high levelbe used.

In the present modification example, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c obtains a pattern indexidxCG which is an index for specifying a context derivation pattern fromsub-block coefficient presence/absence flags in adjacent sub-blocks(right adjacent and lower adjacent sub-blocks), by using the followingEquation (C).

idxCG=significant_coeff_group_flag[xCG+1][yCG]+(significant_coeff_group_flag[xCG][yCG+1]<<1)+(significant_coeff_group_flag[xCG+1][yCG+1]<<2)  (C)

The pattern index idxCG takes values of 0 to 7 from the above Equation(C). The adjacent sub-block coefficient presence/absence contextderiving unit 124 c derives the following five patterns according to thevalues of the pattern index idxCG.

(Pattern 0) In a case where a value of the sub-block coefficientpresence/absence flag is 0 in all of the right adjacent sub-block(xCG+1,yCG), the lower adjacent sub-block (xCG,yCG+1), and the lowerright adjacent sub-block (xCG+1,yCG+1)

(Pattern 1) In a case where a value of the sub-block coefficientpresence/absence flag is 0 in both of the right adjacent sub-block(xCG+1,yCG) and the lower adjacent sub-block (xCG,yCG+1)

(Pattern 2) In a case where a value of the sub-block coefficientpresence/absence flag is 1 in one of the right adjacent sub-block(xCG+1,yCG) and the lower adjacent sub-block (xCG,yCG+1), and a value ofthe sub-block coefficient presence/absence flag is 0 in the otherthereof

(Pattern 3) In a case where a value of the sub-block coefficientpresence/absence flag is 1 in both of the right adjacent sub-block(xCG+1,yCG) and the lower adjacent sub-block (xCG,yCG+1)

(Pattern 4) In a case where a value of the sub-block coefficientpresence/absence flag is 1 in all of the right adjacent sub-block(xCG+1,yCG) the lower adjacent sub-block (xCG,yCG+1), and the lowerright adjacent sub-block (xCG+1,yCG+1)

In the present modification example, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c obtains a pattern indexidxCG by using the above Equation (C), and also derives a context indexin a method illustrated in FIG. 37 according to patterns 0 to 4 obtainedtherefrom.

With reference to FIGS. 37 and 38, a description will be made of aspecific context index derivation method.

FIG. 37 is a diagram illustrating still another example of a pseudo-codefor deriving a context index from coordinates of a process targetfrequency component in a sub-block according to a pattern index idxCGobtained from Equation (C). FIG. 38 illustrates arrangements of valuesof context indexes in the context index derivation method using thepseudo-code illustrated in FIG. 37. In addition, hatched partsillustrated in FIG. 38 are parts which are changed from the arrangementsof values of context indexes illustrated in FIG. 52.

With reference to FIG. 37, a description will be made of a value of acontext index which is derived in each case of patterns 0 to 4.

(Case of Pattern 4)

First, in a case of the pattern 4, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c determines whether or not apattern is the pattern 4. In a case where the pattern is the pattern 4,as illustrated in FIG. 38(e), the adjacent sub-block coefficientpresence/absence context deriving unit 124 c equally derives sigCtx=2 inthe sub-block regardless of values of xB and yB.

In a case where the pattern is not the pattern 4, the adjacent sub-blockcoefficient presence/absence context deriving unit 124 c determineswhether or not the pattern is one of the patterns 0 to 3 in thefollowing. In addition, in FIG. 37, “idxCG&3” is used to calculate lower2 bits of idxCG, and thus values of sub-block coefficientpresence/absence flags of the right adjacent sub-block (xCG+1,yCG) andthe lower adjacent sub-block (xCG,yCG+1) are extracted.

(Case of Pattern 0)

In a case of the pattern 0, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index byusing sigCtx=(xB+yB<=2)<=0) ? 1:0.

In other words, a case of the pattern 0 is the same as a case of thepattern 0 of the above Example. Therefore, values of the context indexesare arranged as illustrated in FIG. 38(a).

(Case of Pattern 1)

In a case of the pattern 1, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index byusing sigCtx=(yB<=1)<=0) ? 1:0.

Consequently, as illustrated in FIG. 38(b), values of the contextindexes are 1 in the first and second rows of the sub-block, and valuesof the context indexes are 0 in the third and fourth rows of thesub-block.

(Case of Pattern 2)

In a case of the pattern 2, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index byusing sigCtx=(xB<=1)<=0) ? 1:0.

Consequently, as illustrated in FIG. 38(c), values of the contextindexes are 1 in the first and second columns of the sub-block, andvalues of the context indexes are 0 in the third and fourth columns ofthe sub-block.

(Case of Pattern 3)

In a case of the pattern 3, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context index byusing sigCtx=(xB+yB<=4)<=0) ? 2:1.

Therefore, in a case of the pattern 3, if a sum of the coordinate xB inthe horizontal direction of the coordinates (xB,yB) in the sub-block andthe coordinate yB in the vertical direction is equal to or smaller than4, a value of a context index is “1”, and, otherwise, a value of acontext index is “0”.

Consequently, values of the context indexes are arranged as illustratedin FIG. 38(d).

As mentioned above, in a cases of the patterns 0 to 3, the contextindexes are respectively arranged as in the examples of the arrangementsillustrated in FIGS. 52(a) to 52(d).

[Operations and Effects]

As mentioned above, the moving image decoding apparatus related toModification Example 7 includes an arithmetic decoding device whichdecodes coded data which is obtained by arithmetically coding varioussyntaxes indicating a transform coefficient with respect to eachtransform coefficient which is obtained for each frequency component byperforming frequency transform on a target image for each unit domain.The arithmetic decoding device includes sub-block splitting means forsplitting a target frequency domain corresponding to a process targetunit domain into sub-blocks each having a predetermined size; sub-blockcoefficient presence/absence flag decoding means for decoding asub-block coefficient presence/absence flag indicating whether or not atleast one non-zero transform coefficient is included in the sub-blockwith respect to the respective sub-blocks into which the frequencydomain is split by the sub-block splitting means; adjacent sub-blockcoefficient presence determining means for determining whether or not atleast one non-zero transform coefficient is included in each ofsub-blocks adjacent to a process target sub-block on the basis of thesub-block coefficient presence/absence flag; and context index derivingmeans for deriving a context index assigned to a transform coefficientpresence/absence flag which is syntax indicating whether or not thetransform coefficient is 0, in which, in a case where at least onenon-zero transform coefficient is included in sub-blocks of apredetermined number or more as a result of the determination, thecontext index deriving means derives the context index corresponding toa case where an occurrence probability of a non-zero transformcoefficient is high, equally in the process target sub-block.

According to the configuration, as adjacent sub-blocks which are targetsfor determining a sub-block coefficient presence/absence flag, the lowerright adjacent sub-block C is further used in addition to the rightadjacent sub-block A and the lower adjacent sub-block B.

It is determined whether or not a state occurs in which an occurrenceprobability of a non-zero transform coefficient is equally high in theprocess target sub-block X on the basis of states of the sub-blockcoefficient presence/absence flags of the target adjacent sub-blocks.

In addition, in a case where the state occurs in which an occurrenceprobability of a non-zero transform coefficient is equally high in theprocess target sub-block X, a context index corresponding to a casewhere an occurrence probability of a non-zero transform coefficient ishigh is equally used in the process target sub-block X. Therefore, it ispossible to improve coding efficiency.

In the above description, in a case where values of the sub-blockcoefficient presence/absence flags are 1 in all the adjacent sub-blocks,a context index corresponding to a case where an occurrence probabilityof a non-zero transform coefficient is high is equally used, but thepresent invention is not limited thereto.

In a case where values of sub-block coefficient presence/absence flagsare 1 in adjacent sub-blocks of a predetermined number or more, acontext index corresponding to a case where an occurrence probability ofa non-zero transform coefficient is high may be equally used. In a casewhere values of sub-block coefficient presence/absence flags are 1 inadjacent sub-blocks of a predetermined number or more, it can be saidthat an occurrence probability of a non-zero transform coefficient isequally in a high state in the process target sub-block X. Therefore,the corresponding configuration can achieve the same effect as theconfiguration of Modification Example 5 described above.

Modification Example 8

NPL 3 has proposed a method in which, in an 8×8 TU, shapes of sub-blockswhich are different from each other in a scan direction are unified intoa 4×4 sub-block; also in an 8×8 TU to 32×32 TU, a derivation pattern isselected according to whether or not a non-zero transform coefficient ispresent in an adjacent sub-block; and a context index regardingtransform coefficient presence/absence flag is derived from a positionin a sub-block according to the selected derivation pattern. Inaddition, NPL 3 has proposed a method in which, in relation to an 8×8 TUfor luminance, context regarding a transform coefficientpresence/absence flag is differentiated in cases where a scan directionis an up-right diagonal scan and a horizontal scan or a vertical scan.

However, in a case of luminance of an 8×8 TU, the horizontal fast scanand vertical fast scan appear only in intra-prediction, and a usefrequency thereof is lower than the up-right diagonal scan. In addition,a tendency (an average of occurrence frequencies of non-zero transformcoefficients during the horizontal fast scan and the vertical fast scan)of an occurrence frequency of a non-zero transform coefficient at acoefficient position in a sub-block corresponding to each index patternidxCG of the horizontal fast scan and the vertical fast scan is highlysimilar to a tendency of an occurrence frequency of a non-zero transformcoefficient during the up-right diagonal scan. Accordingly, contextsregarding transform coefficient presence/absence flags during theup-right diagonal scan, the horizontal fast scan, and the vertical fastscan in luminance of an 8×8 TU can be shared thereamong.

Hereinafter, with reference to FIGS. 65, 66, 67 and 68, a descriptionwill be made of Modification Example 8 in which derivation of a contextindex regarding a transform coefficient presence/absence flag in an 8×8TU is simplified, and thus the number of contexts regarding thetransform coefficient presence/absence flags is reduced.

FIG. 65 is a flowchart illustrating an operation of deriving a contextindex regarding a transform coefficient presence/absence flag in thecoefficient presence/absence flag coding unit 124 related toModification Example 8.

(Step SX101)

The TU size determining unit 124 a determines whether or not a processtarget TU size is smaller than a predetermined size (for example, an 8×8TU). In a case where the process target TU size is smaller than thepredetermined size (YES in step SX101), the TU size determining unit 124a selects the position context deriving unit 124 b as context derivingmeans, and the flow proceeds to step SX104. In other cases, the flowproceeds to step SX102 (No in step SX101).

For example, the following Expression is used for determination. log2TrafoSize<THSize is used, and, for example, 3 is used as THSize. In acase where 3 is used as the threshold value THsize, it is determinedthat a 4×4 TU is smaller than the predetermined size. It is determinedthat 8×8 TU, 16×4 TU, 4×16 TU, 16×16 TU, 32×4 TU, 4×32 TU, and 32×32 TUare equal to or larger than the predetermined size.

(Step SX102)

In a case where the process target TU size is equal to or larger thanthe predetermined size (for example, an 8×8 size) (No in step SX101),the TU size determining unit 124 a determines whether or not a positionof a process target transform coefficient is DC. In a case where theposition of a process target transform coefficient is DC (Yes in stepSX102), the TU size determining unit 124 a selects the position contextderiving unit 124 b as context deriving means, and the flow proceeds tostep SX104. In other cases, the TU size determining unit 124 a selectsthe adjacent sub-block coefficient presence/absence context derivingunit 124 c as context deriving means, and the flow proceeds to stepSX103 (No in step SX102). In addition, whether or not the position of aprocess target transform coefficient is DC may be determined on thebasis of whether or not a sum of xC and yC is the same as 0 by using aposition (xC,yC) of a transform coefficient. In other words, thedetermination may be performed on the basis of determination of whether“xC+yC==0” is true or false.

(Step SX104)

In a case where the process target TU size is smaller the predeterminedsize (for example, an 8×8 TU) (Yes in step SX101), or the position ofthe process target transform coefficient is DC (Yes in step SX102), theposition context deriving unit 124 b selected as context deriving meansderives a context index ctxIdx of a transform coefficientpresence/absence flag corresponding to a position (xC,yC) of thetransform coefficient illustrated in FIG. 66. FIG. 66 is a diagramillustrating a context index assigned to each coefficient position inluminance or chroma in a 4×4 TU. As illustrated in FIG. 66, the 4×4 TUis split into nine domains including “0” to “8”, and a context index isassigned to each of the nine domains. Therefore, the number of contextsof the 4×4 TU is “9”. Further, in a case where the position of theprocess target transform coefficient is DC, a value assigned to a DCcomponent of the 4×4 TU in FIG. 66 is assigned as a context index whichis common to TUs including the 4×4 TU to a 32×32 TU.

(Step SX103)

In a case where the process target TU size is smaller the predeterminedsize (for example, an 8×8 TU) (No in step SX101), or the position of theprocess target transform coefficient is DC (Yes in step SX102), theadjacent sub-block coefficient presence/absence context deriving unit124 c selected as context deriving means selects a derivation patternaccording to whether or not a non-zero transform coefficient is presentin an adjacent sub-block, and derives a context index sigCtx (ctxIdx)regarding a transform coefficient presence/absence flag from a positionin the sub-block according to the selected derivation pattern.

A more specific process in which the adjacent sub-block coefficientpresence/absence context deriving unit 124 c derives a context indexctxIdx regarding a transform coefficient presence/absence flag in stepSX103 is as follows.

(Step SX103-1)

The adjacent sub-block coefficient presence/absence context derivingunit 124 c obtains a pattern index idxCG corresponding to the derivationpattern according to whether or not a non-zero transform coefficient ispresent in the adjacent sub-block. The pattern index idxCG may beobtained from the above Equation (A).

(Step SX103-2)

A context index sigCtx (ctxIdx) regarding a transform coefficientpresence/absence flag is derived from the derivation patterncorresponding to the obtained pattern index idxCG and the position inthe sub-block. The derivation pattern corresponding to the pattern indexidxCG may use, for example, that of Modification Example 5-1 describedabove, and thus detailed description thereof will be omitted. In otherwords, in a case where the pattern index idxCG is the pattern 0, valuesof context indexes have the arrangement as illustrated in FIG. 29(a). Ina case where the pattern index idxCG is the pattern 1, values of contextindexes have the arrangement as illustrated in FIG. 29(b). In a casewhere the pattern index idxCG is the pattern 2, values of contextindexes have the arrangement as illustrated in FIG. 29(c). In a casewhere the pattern index idxCG is the pattern 3, values of contextindexes have the arrangement as illustrated in FIG. 29(d).

(Step SX103-3)

The adjacent sub-block coefficient presence/absence context derivingunit 124 c adds a predetermined offset value to the context index sigCtx(ctxIdx) obtained in step SX103-2, so as to derive the context indexsigCtx (ctxIdx) regarding a process target transform coefficient.

Hereinafter, derivation of the predetermined offset value in stepSX103-3 will be described by exemplifying luminance. FIG. 67 is aflowchart illustrating a more detailed operation of step SX103-3.

(Step SX201)

It is determined whether or not a process target sub-block position(xCG,yCG) is located in a high frequency. For example, the determinationmay be performed on the basis of xCG+yCG>TH1. In a case where a sum ofxCG and yCG is larger than a predetermined threshold value TH1, it isdetermined that the position is located in a high frequency, and,otherwise, it is determined that the position is located in a lowfrequency. The threshold value TH1 may be 0, for example. In this case,a sub-block including a DC component is treated as a low frequency.

(Step SX202)

In a case where the process target sub-block position (xCG,yCG) islocated in a high frequency (Yes in step SX201), a predetermined offsetvalue offsetHighFreq for identifying contexts for a low frequency and ahigh frequency is added to the context index sigCtx (ctxIdx). In otherwords, sigCtx (ctxIdx) is obtained by sigCtx=sigCtx+offsetHighFreq. Inaddition, as a meaning of the operator “+=” shown in step SX202 of FIG.67, in a case where A and B are used such as “A+=B”, this indicates“A=A+B”. The same applies hereinafter.

In addition, in the present example, an occurrence frequency of anon-zero transform coefficient is indicated in three levels including“high”, “intermediate”, and “low”, and thus “3” is used as thepredetermined offset value offsetHighFreq.

(Step SX203)

It is determined whether or not a process target TU size is apredetermined size (for example, an 8×8 TU). In other words, it isdetermined whether or not a process target TU size is a predeterminedsize by determining whether log 2TrafoSize==THSize is true or false.

In addition, for example, “3” indicating a size of an 8×8 TU is used asthe threshold value THSize.

(Step SX204)

In a case where the process target TU size is the predetermined size(for example, an 8×8 TU) (Yes in step SX203), a predetermined offsetvalue offsetNA for identifying contexts for a TU satisfying thethreshold value THSize and other TUs is added to the context indexctxIdx. In other words, sigCtx=sigCtx+offsetNA is computed.

Here, in order to identify contexts for a 4×4 TU and an 8×8 TU, theoffset value offsetNA is set to, for example, “9” which is the number ofcontexts of the 4×4 TU illustrated in FIG. 66.

(Step Sx205)

In a case where the process target TU size is not the predetermined size(for example, an 8×8 TU) (No in step SX203), a predetermined offsetvalue offsetNB for identifying contexts for a TU (8×8 TU) satisfying thethreshold value THSize and other TUs (a 16×16 TU to a 32×32 TU) is addedthereto. In other words, sigCtx=sigCtx+offsetNB is computed. Here, inorder to identify contexts for an 8×8 TU and a 16×16 TU to a 32×32 TU,the offset value offsetNB is set to, for example, “15” which is a sum of“9” as the number of contexts of the 4×4 TU illustrated in FIG. 66 and“6” as the number of contexts of the 8×8 TU. The reason why the numberof contexts of the 8×8 TU is “6” is that, in the present example, anoccurrence frequency of a non-zero transform coefficient is indicated inthree levels including “high”, “intermediate”, and “low”, and each of alow frequency and a high frequency has “three” as the number ofcontexts.

As mentioned above, in Modification Example 8, if the offset valuesoffsetHighFreq, offsetNA, and offsetNB for identifying context indexesare set to offsetHighFreq=3, offsetNA=9, and offsetNB=15, the contextindexes regarding transform coefficient presence/absence flags forluminance are assigned with values of 0 to 20 as illustrated in FIG. 68.

-   -   ctxIdx=0 is a context index for DC    -   ctxIdx=1 to 8 is context indexes for a 4×4 TU    -   ctxIdx=9 to 11 is context indexes for an 8×8 TU (low frequency)    -   ctxIdx=12 to 14 is context indexes for an 8×8 TU (high        frequency)    -   ctxIdx=15 to 17 is context indexes for a 16×16 TU to a 32×32 TU        (low frequency)    -   ctxIdx=18 to 20 is context indexes for a 16×16 TU to a 32×32 TU        (high frequency)

Therefore, a total number of contexts is 21.

Here, advantages of the configuration will be described throughcomparison with a comparative example (NPL 3) of the related art.

<Description of Comparative Technique>

Hereinafter, a description will be made of derivation of a context indexregarding a transform coefficient presence/absence flag in a coefficientpresence/absence flag coding unit related to the comparative technique(NPL 3).

In Modification Example 8 and NPL 3, a flow of a method of selectingcontext deriving means, illustrated in FIG. 65, is common thereto, andthus description thereof will be omitted. In addition, in step SX103 ofFIG. 65, the processes in steps SX103-1 and SX103-2 are common to theModification Example 8 and the comparative technique, and thus detaileddescription thereof will be omitted. In other words, also in thecomparative technique, a pattern index idxCG corresponding to aderivation pattern is derived on the basis of the above Equation (X)according to determines whether or not a non-zero transform coefficientis present in an adjacent sub-block. Then, a context index regarding atransform coefficient presence/absence flag is derived from thederivation pattern corresponding to the derived pattern index idxCG anda position in a sub-block. The derivation pattern corresponding to thepattern index idxCG is the same as in Modification Example 5-1 describedabove, and thus detailed description thereof will be omitted.

In a case where the pattern index idxCG is the pattern 0, values ofcontext indexes have the arrangement as illustrated in FIG. 29(a). In acase where the pattern index idxCG is the pattern 1, values of contextindexes have the arrangement as illustrated in FIG. 29(b). In a casewhere the pattern index idxCG is the pattern 2, values of contextindexes have the arrangement as illustrated in FIG. 29(c). In a casewhere the pattern index idxCG is the pattern 3, values of contextindexes have the arrangement as illustrated in FIG. 29(d).

Hereinafter, with reference to FIG. 74, a detailed description will bemade of an operation of adding an offset of each condition to a contextindex which is obtained from a derivation pattern corresponding to apattern index idxCG and a position in a sub-block in step SX103-3 ofFIG. 65 in the comparative technique.

A description will be made how the derivation of a predetermined offsetvalue corresponding to step SX103-3 of FIG. 65 is performed in thecomparative example, by exemplifying a case of luminance. As illustratedin FIG. 74, in the comparative technique, a process SX103-3Pcorresponding to step SX103-3 of FIG. 65 is performed as follows.

(Step SY201)

It is determined whether or not a process target sub-block position(xCG,yCG) is located in a high frequency.

(Step SY202)

In a case where the process target sub-block position (xCG,yCG) islocated in a high frequency (Yes in step SY201), a predetermined offsetvalue for identifying contexts for a low frequency and a high frequencyis added to the context index sigCtx. In NPL 3, sigCtx is calculated bysigCtx=sigCtx+3.

(Step SY203)

It is determined whether or not a process target TU size is an 8×8 TU.

(Step SY204)

In a case where the process target TU size is the 8×8 TU (Yes in stepSY203), it is determined that a scan direction is the up-right diagonalscan.

(Step SY205)

In a case where a scan direction is the up-right diagonal scan in theprocess target TU (Yes in step SY204), a predetermined offset value foridentifying contexts for the up-right diagonal scan and the horizontalfast scan or the vertical fast scan is added to the context indexctxIdx. In the comparative technique, sigCtx is calculated bysigCtx=sigCtx+9.

(Step SY206)

In a case where a scan direction is not the up-right diagonal scan inthe process target TU, that is, a scan direction is the horizontal fastscan or the vertical fast scan (No in step SY204), a predeterminedoffset value for identifying contexts for the up-right diagonal scan andthe horizontal fast scan or the vertical fast scan is added to thecontext index ctxIdx. In the comparative technique, sigCtx is calculatedby sigCtx=sigCtx+15.

(Step SY207)

In a case where the process target TU size is not an 8×8 TU, that is,the size is 16×16, 32×32, 4×16, 16×4, 8×32, or 32×8 (No in step SY203),a predetermined offset value for identifying contexts for the 8×8 TU andanother TU is added thereto. In the comparative technique, sigCtx iscalculated by sigCtx=sigCtx+21.

As mentioned above, in the comparative technique, the context indexesregarding transform coefficient presence/absence flags for luminance areassigned with values of 0 to 26 as illustrated in FIG. 69.

-   -   ctxIdx=0 is a context index for DC    -   ctxIdx=1 to 8 is context indexes for a 4×4 TU    -   ctxIdx=9 to 11 is context indexes for up-right diagonal scan of        an 8×8 TU (low frequency)    -   ctxIdx=12 to 14 is context indexes for up-right diagonal scan of        an 8×8 TU (high frequency)    -   ctxIdx=15 to 17 is context indexes for horizontal fast scan or        vertical fast scan of an 8×8 TU (low frequency)    -   ctxIdx=18 to 20 is context indexes for horizontal fast scan or        vertical fast scan of an 8×8 TU (high frequency)    -   ctxIdx=21 to 23 is context indexes for a 16×16 TU to a 32×32 TU        (low frequency)    -   ctxIdx=24 to 26 is context indexes for a 16×16 TU to a 32×32 TU        (high frequency)

Therefore, a total number of contexts is 27.

In the comparative technique, in relation to the 8×8 TU for luminance,contexts regarding transform coefficient presence/absence flags aredifferentiated from each other in cases where a scan direction is theup-right diagonal scan and the horizontal fast scan or the vertical fastscan. On the other hand, in Modification Example 8, by the use ofcharacteristics in which a tendency (an average of occurrencefrequencies of non-zero transform coefficients during the horizontalfast scan and the vertical fast scan) of an occurrence frequency of anon-zero transform coefficient at a coefficient position in a sub-blockcorresponding to each index pattern idxCG of the horizontal fast scanand the vertical fast scan is highly similar to a tendency of anoccurrence frequency of a non-zero transform coefficient during theup-right diagonal scan, contexts regarding transform coefficientpresence/absence flags during the up-right diagonal scan, the verticalfast scan, and the horizontal fast scan in the luminance of the 8×8 TUare shared thereamong. Therefore, branch regarding changes in contextaccording to a scan direction can be reduced, and a total number ofcontext indexes regarding transform coefficient presence/absence flagsfor the luminance can be reduced from 27 to 21, that is, by a totalnumber of six, when compared with the comparative technique. Thus, it ispossible to reduce a memory size required to maintain a state ofcontext. In addition, it has been confirmed from the test by the presentinventor that, in a case where the patterns illustrated in FIGS. 29(a)to 29(d) are used as derivation patterns corresponding to the patternindex idxCG, there is no reduction in coding efficiency due to thesharing of contexts regarding transform coefficient presence/absenceflags during the up-right diagonal scan, the horizontal fast scan, andthe vertical fast scan in luminance of the 8×8 TU including respectivecontext indexes.

[Operations and Effects]

As mentioned above, according to Modification Example 8, it is possibleto achieve effects of minimizing a reduction in coding efficiency,simplifying a process of deriving a context index regarding a transformcoefficient presence/absence flag, and reducing a memory size through areduction in the number of contexts.

Modification Example 8-1

In Modification Example 8, as arrangements of context indexes in asub-block, corresponding to a pattern index idxCG from an 8×8 TU to a32×32 TU, the patterns illustrated in FIGS. 29(a) to 29(d) are used inthe same manner as in Modification Example 5-1, but the presentinvention is not limited thereto.

According to the test by the present inventor, the following fact hasbeen confirmed as a tendency of an average occurrence frequency of anon-zero transform coefficient during the up-right diagonal scan, thehorizontal fast scan, and the vertical fast scan, in the luminance of an8×8 TU to a 32×32 TU.

In other words, in a case where the pattern index idxCG is a pattern 0,that is, a value of the sub-block coefficient presence/absence flag is 0in both of the right adjacent sub-block (xCG+1,yCG) and the loweradjacent sub-block (xCG,yCG+1), there are the following tendencies P0-1to P0-3.

-   -   P0-1: An occurrence frequency of a non-zero transform        coefficient is high on average at a position where a coefficient        position (xB,yB) in a sub-block satisfies xB+yB<2.    -   P0-2: An occurrence frequency of a non-zero transform        coefficient is approximately intermediate at a position where a        coefficient position (xB,yB) in a sub-block satisfies 2≤xB+yB<3        or 2≤xB+yB<4.    -   P0-3: An occurrence frequency of a non-zero transform        coefficient is low at a position where a coefficient position        (xB,yB) in a sub-block satisfies xB+yB>3 or xB+yB>4.

Therefore, in consideration of the tendencies, in an 8×8 TU to a 32×32TU, context indexes in the pattern 0 may be arranged as illustrated inFIG. 61(a) of Modification Example 5-6 or as illustrated in FIG. 63(a)of Modification Example 5-7.

In a case of FIG. 61(a), a context index can be derived from thefollowing Equation.

sigCtx=(xB+yB<2) ? 2:(xB+yB<3) ? 1:0

In a case of FIG. 63(a), a context index can be derived from thefollowing Equation.

sigCtx=(xB+yB<2) ? 2:(xB+yB<4) ? 1:0

Hereinafter, whether the determination is performed in “x or less” or“x+1 below” may be changed as appropriate.

In a case where the pattern index idxCG is a pattern 1, that is, a valueof the sub-block coefficient presence/absence flag is 0 in the rightadjacent sub-block (xCG+1,yCG) and a value of the sub-block coefficientpresence/absence flag is 1 in the lower adjacent sub-block (xCG,yCG+1),there are the following tendencies P1-1 to P1-3.

-   -   P1-1: An occurrence frequency of a non-zero transform        coefficient is high on average at a position where a coefficient        position (xB,yB) in a sub-block satisfies yB<1.    -   P1-2: An occurrence frequency of a non-zero transform        coefficient is approximately intermediate at a position where a        coefficient position (xB,yB) in a sub-block satisfies 1≤yB<2 or        1≤yB<3.    -   P1-3: An occurrence frequency of a non-zero transform        coefficient is low at a position where a coefficient position        (xB,yB) in a sub-block satisfies yB≥2 or yB≥3.

Therefore, in consideration of the tendencies, in an 8×8 TU to a 32×32TU, context indexes in the pattern 1 may be arranged as illustrated inFIG. 33(b) instead of FIG. 29(b).

In a case of FIG. 33(b), a context index can be derived from thefollowing Equation.

sigCtx=(yB<1) ? 2:(yB<3) ? 1:0

If the configuration is applied to the pattern 1, in the same manner asin Modification Example 8, it is possible to minimize a reduction incoding efficiency and to simplify derivation of a context indexregarding a transform coefficient presence/absence flag.

In a case where the pattern index idxCG is a pattern 2, that is, a valueof the sub-block coefficient presence/absence flag is 0 in the rightadjacent sub-block (xCG+1,yCG) and a value of the sub-block coefficientpresence/absence flag is 1 in the lower adjacent sub-block (xCG,yCG+1),there are the following tendencies P2-1 to P2-3.

-   -   P2-1: An occurrence frequency of a non-zero transform        coefficient is high on average at a position where a coefficient        position (xB,yB) in a sub-block satisfies xB<1.    -   P2-2: An occurrence frequency of a non-zero transform        coefficient is approximately intermediate at a position where a        coefficient position (xB,yB) in a sub-block satisfies 1≤XB<2 or        1≤XB<3.    -   P2-3: An occurrence frequency of a non-zero transform        coefficient is low at a position where a coefficient position        (xB,yB) in a sub-block satisfies xB≥2 or xB≥3.

Therefore, in consideration of the tendencies, in an 8×8 TU to a 32×32TU, context indexes in the pattern 2 may be arranged as illustrated inFIG. 33(c) instead of FIG. 29 (c).

In a case of FIG. 33(c), a context index can be derived from thefollowing Equation.

sigCtx=(xB<1) ? 2:(xB<3) ? 1:0

If the configuration is applied to the pattern 2, in the same manner asin Modification Example 8, it is possible to minimize a reduction incoding efficiency and to simplify derivation of a context indexregarding a transform coefficient presence/absence flag.

In a case where the pattern index idxCG is a pattern 3, that is, a valueof the sub-block coefficient presence/absence flag is 1 in the rightadjacent sub-block (xCG+1,yCG) and a value of the sub-block coefficientpresence/absence flag is 1 in the lower adjacent sub-block (xCG,yCG+1),there are the following tendency P3-1.

-   -   P3-1: An occurrence frequency of a non-zero transform        coefficient is high on average or approximately intermediate        regardless of a position where a coefficient position (xB,yB) in        a sub-block.

Therefore, in consideration of the tendency, in an 8×8 TU to a 32×32 TU,“1” indicating that an occurrence frequency of a non-zero transformcoefficient is approximately intermediate may be used instead of “2”indicating that an occurrence frequency of a non-zero transformcoefficient is high, in FIG. 29(d) illustrating the arrangement ofcontext indexes in the pattern 3.

In this case, a context index may be derived from the followingEquation. sigCtx=1

[Operations and Effects]

[[As to Pattern 0]]

As mentioned above, according to the configuration of ModificationExample 8-1, in the moving image decoding apparatus 1, the context indexderiving means determines a sub-block coefficient presence/absence flagfor a right adjacent sub-block which is a sub-block adjacent to theright side and a lower adjacent sub-block which is adjacent to the lowerside. When it is determined that a non-zero transform coefficient is notpresent in either the right adjacent sub-block or the lower adjacentsub-block, on the basis of the determination result, the context indexderiving means derives the context index corresponding to a case wherean occurrence probability of a non-zero transform coefficient is high ina case where a sum of xB and yB indicating a coefficient position in asub-block is equal to or smaller than a first threshold value; derivesthe context index corresponding to a case where an occurrenceprobability of a non-zero transform coefficient is intermediate in acase where the sum of xB and yB is greater than the first thresholdvalue and is equal to or smaller than a second threshold value; andderives the context index corresponding to a case where an occurrenceprobability of a non-zero transform coefficient is low in a case wherethe sum of xB and yB is greater than the second threshold value. Since acontext derivation pattern which is more suitable for an actualoccurrence probability of a transform coefficient can be realized, it ispossible to further minimize a reduction in coding efficiency and tosimplify derivation of a context index. Particularly, by setting thefirst threshold value to 2 and the second threshold value to 3, it ispossible to derive a preferable context index which is more suitable foran actual occurrence probability of a non-zero transform coefficient.Particularly, in a case where derivation of a context index is made incommon to TUs including an 8×8 TU to a 32×32 TU, it is possible toderive a preferable context index which is more suitable for an actualoccurrence probability of a non-zero transform coefficient by settingthe first threshold value to 1 and the second threshold value to 2. Inaddition, the first threshold value may be set to 2, and the secondthreshold value may be set to 3.

[[As to Patterns 1 and 2]]

As mentioned above, according to the configuration of ModificationExample 8-1, in the moving image decoding apparatus 1, the context indexderiving means determines a sub-block coefficient presence/absence flagfor a right adjacent sub-block which is a sub-block adjacent to theright side and a lower adjacent sub-block which is adjacent to the lowerside. When it is determined that a non-zero transform coefficient is notpresent in one of the right adjacent sub-block and the lower adjacentsub-block, the context index deriving means selects a coefficientposition of one of xB and yB indicating a coefficient position in asub-block in an adjacent direction of a sub-block in which it isdetermined that a non-zero transform coefficient is not present; derivesthe context index corresponding to a case where an occurrenceprobability of a non-zero transform coefficient is high in a case wherethe coefficient position is equal to or smaller than a first thresholdvalue; derives the context index corresponding to a case where anoccurrence probability of a non-zero transform coefficient isintermediate in a case where the coefficient position is greater thanthe first threshold value and is equal to or smaller than a secondthreshold value; and derives the context index corresponding to a casewhere an occurrence probability of a non-zero transform coefficient islow in a case where the coefficient position is greater than the secondthreshold value. Since a context derivation pattern which is moresuitable for an actual occurrence probability of a transform coefficientcan be realized, it is possible to minimize a reduction in codingefficiency and to simplify derivation of a context index. Particularly,in a case where derivation of a context index is made in common to TUsincluding an 8×8 TU to a 32×32 TU, it is possible to derive a preferablecontext index which is more suitable for an actual occurrenceprobability of a non-zero transform coefficient by setting the firstthreshold value to 0 and the second threshold value to 1. In addition,the first threshold value may be set to 0, and the second thresholdvalue may be set to 2.

[[As to Pattern 3] ]

As mentioned above, according to the configuration of ModificationExample 8-1, in the moving image decoding apparatus 1, the context indexderiving means determines a sub-block coefficient presence/absence flagfor a right adjacent sub-block which is a sub-block adjacent to theright side of a process target sub-block and a lower adjacent sub-blockwhich is adjacent to the lower side thereof. When it is determined thata non-zero transform coefficient is present in both the right adjacentsub-block and the lower adjacent sub-block with respect to a processtarget sub-block, the context index deriving means derives a fixedcontext index with respect to a non-zero transform coefficient in theprocess target sub-block on the basis of the determination result.Particularly, a context index of a non-zero transform coefficient whichis fixedly derived is preferably set to a context index indicating thatan occurrence probability of a non-zero transform coefficient is high.In addition, a context index of a non-zero transform coefficient whichis fixedly derived is also preferably set to a context index indicatingthat an occurrence probability of a non-zero transform coefficient isapproximately intermediate. Consequently, since a fixed context indexwhich is more suitable for an actual occurrence probability of atransform coefficient can be derived, it is possible to minimize areduction in coding efficiency and to simplify derivation of a contextindex.

Modification Example 8-2

In Modification Examples 8 and 8-1, arrangements of context indexes in asub-block corresponding to a pattern index idxCG are made in common toan 8×8 TU to a 32×32 TU, but the present invention is not limitedthereto. Arrangements of context indexes of patterns 0 to 2 may beadaptively changed in accordance with a scan direction (scan indexscanIdx). Therefore, an arrangement of context indexes is changed inconsideration of a bias of an occurrence frequency of a non-zerotransform coefficient for each scan direction, and thus it is possibleto improve coding efficiency when compared with Modification Examples 8and 8-1. In addition, in a case of Modification Example 8-2, it isassumed that a scan direction (scan index scanIdx) is input to theadjacent sub-block coefficient presence/absence context deriving unit124 c from an external device.

FIG. 70 illustrates an example of a pseudo-code for deriving a contextindex corresponding to each pattern index idxCG in a case where anarrangement of context indexes in a sub-block is changed in accordancewith a scan direction (scan index scanIdx).

According to the test by the present inventor, the following fact hasbeen confirmed as each tendency of an occurrence frequency of a non-zerotransform coefficient in a pattern 0 during the up-right diagonal scan,the horizontal fast scan, and the vertical fast scan, in an 8×8 TU.

<Case of Up-Right Diagonal Scan (scanIdx==0)>

-   -   An occurrence frequency of a non-zero transform coefficient is        high on average at a position where a coefficient position        (xB,yB) in a sub-block satisfies xB+yB<2.    -   An occurrence frequency of a non-zero transform coefficient is        approximately intermediate at a position where a coefficient        position (xB,yB) in a sub-block satisfies 2<xB+yB<3.    -   An occurrence frequency of a non-zero transform coefficient is        low at a position where a coefficient position (xB,yB) in a        sub-block satisfies xB+yB>3.

Therefore, in consideration of the tendencies, context indexes in thepattern 0 during the up-right diagonal scan are preferably arranged asillustrated in FIG. 71(a).

In a case of FIG. 71(a), a context index can be derived from thefollowing Equation.

sigCtx=(xB+yB<2) ? 2:(xB+yB<3) ? 1:0

In addition, the above Equation may be expanded to be represented as thefollowing Equation.

sigCtx=(xB+yB<TH1) ? 2:(xB+yB<TH2) ? 1:0

In other words, in a case where xB+yB is smaller than the thresholdvalue TH1, a context index indicating that an occurrence frequency of anon-zero transform coefficient is high is derived; in a case where xB+yBis equal to or greater than the threshold value TH1 and is smaller thanthe threshold value TH2, a context index indicating that an occurrencefrequency of a non-zero transform coefficient is approximatelyintermediate is derived; and in other cases (in a case where xB+yB isgreater than the threshold value TH2), a context index indicating thatan occurrence frequency of a non-zero transform coefficient is low isderived.

A case of FIG. 71(a) is a case of the threshold value TH1=2 and TH2=3.

<Case of Horizontal Fast Scan (scanIdx==1)>

In a case of the horizontal fast scan, there is a tendency for non-zerotransform coefficients to concentrate on frequency components in thehorizontal direction. Particularly, in a case of the pattern 0, thereare the following tendencies.

-   -   An occurrence frequency of a non-zero transform coefficient is        high on average at a position where a coefficient position        (xB,yB) in a sub-block satisfies xB+2×yB<3.    -   An occurrence frequency of a non-zero transform coefficient is        approximately intermediate at a position where a coefficient        position (xB,yB) in a sub-block satisfies 3<xB+2×yB<5.    -   An occurrence frequency of a non-zero transform coefficient is        low at a position where a coefficient position (xB, yB) in a        sub-block satisfies xB+2×yB>5.

Therefore, in consideration of the tendencies, context indexes in thepattern 0 during the vertical fast scan are preferably arranged asillustrated in FIG. 71(b).

In a case of FIG. 71(b), a context index can be derived from thefollowing Equation.

sigCtx=(xB+2*yB<3) ? 2:(xB+2*yB<5) ? 1:0

In addition, the above Equation may be expanded to be represented as thefollowing Equation.

sigCtx=(W1*xB+W2*yB<TH3) ? 2:(W1*xB+W2*yB<TH4) ? 1:0

In other words, in a case where the weighted sum “W1×xB+W2×yB” issmaller than the threshold value TH3, a context index indicating that anoccurrence frequency of a non-zero transform coefficient is high isderived; in a case where the weighted sum “W1×xB+W2×yB” is equal to orgreater than the threshold value TH3 and is smaller than the thresholdvalue TH4, a context index indicating that an occurrence frequency of anon-zero transform coefficient is approximately intermediate is derived;and in other cases (in a case where the weighted sum “W1×xB+W2×yB” isgreater than the threshold value TH4), a context index indicating thatan occurrence frequency of a non-zero transform coefficient is low isderived.

A case of FIG. 71(b) is a case of the weighting factor W1=1, theweighting factor W2=2, the threshold value TH3=3, and the thresholdvalue TH4=5. In addition, in a case of the horizontal fast scan, sincenon-zero transform coefficients concentrate in the horizontal direction,the weighting factor is set to W1=1, the weighting factor is set toW2=1, the threshold value is set to TH3=1, and the threshold value isset to TH4=2, so that a weighted sum is simplified, and thus the contextindexes illustrated in FIG. 29(b) may be derived. In addition, bysetting the weighting factor to W1=1, the weighting factor to W2=3, thethreshold value to TH3=4, and the threshold value to TH4=8, anarrangement of context indexes illustrated in FIG. 72(a) may beobtained.

<Case of Vertical Fast Scan (scanIdx==2)>

In a case of the vertical fast scan, there is a tendency for non-zerotransform coefficients to concentrate on frequency components in thevertical direction. Particularly, in a case of the pattern 0, there arethe following tendencies.

-   -   An occurrence frequency of a non-zero transform coefficient is        high on average at a position where a coefficient position        (xB,yB) in a sub-block satisfies 2×xB+yB<3.    -   An occurrence frequency of a non-zero transform coefficient is        approximately intermediate at a position where a coefficient        position (xB,yB) in a sub-block satisfies 3<2×xB+yB<5.    -   An occurrence frequency of a non-zero transform coefficient is        low at a position where a coefficient position (xB,yB) in a        sub-block satisfies 2×xB+yB>5.

Therefore, in consideration of the tendencies, context indexes in thepattern 0 during the vertical fast scan are preferably arranged asillustrated in FIG. 71(c).

In a case of FIG. 71(c), a context index can be derived from thefollowing Equation.

sigCtx=(2*xB+yB<3) ? 2:(2*xB+yB<5) ? 1:0

In addition, the above Equation may be expanded to be represented as thefollowing Equation.

sigCtx=(W3*xB+W4*yB<TH5) ? 2:(W3*xB+W4*yB<TH6) ? 1:0

In other words, in a case where the weighted sum “W3×xB+W4×yB” issmaller than the threshold value TH5, a context index indicating that anoccurrence frequency of a non-zero transform coefficient is high isderived; in a case where the weighted sum “W3×xB+W4×yB” is equal to orgreater than the threshold value TH5 and is smaller than the thresholdvalue TH6, a context index indicating that an occurrence frequency of anon-zero transform coefficient is approximately intermediate is derived;and in other cases (in a case where the weighted sum “W3×xB+W4×yB” isgreater than the threshold value TH6), a context index indicating thatan occurrence frequency of a non-zero transform coefficient is low isderived.

A case of FIG. 71(c) is a case of the weighting factor W3=2, theweighting factor W4=1, the threshold value TH5=3, and the thresholdvalue TH6=5. In addition, in a case of the horizontal fast scan, sincenon-zero transform coefficients concentrate in the vertical direction,the weighting factor is set to W1=1, the weighting factor is set toW2=1, the threshold value is set to TH5=1, and the threshold value isset to TH6=2, so that a weighted sum is simplified, and thus the contextindexes illustrated in FIG. 29(c) may be derived. In addition, bysetting the weighting factor to W1=3, the weighting factor to W2=1, thethreshold value to TH5=4, and the threshold value to TH6=8, anarrangement of context indexes illustrated in FIG. 72(b) may beobtained.

(In Cases of Patterns 1 to 3)

As illustrated in FIGS. 71(d) to 71(f), there are the same derivationmethod and arrangements of the same values as in the ModificationExample 5-1 of FIGS. 29(b), 29(c) and 29(d).

In addition, the patterns 1 to 3 may have the same derivation method andarrangements of the same values as the patterns 1 to 3 in any one ofModification Examples 5-1 to 5-7.

Further, also in the patterns 1 and 2, in consideration a bias of anon-zero transform coefficient due to a directivity for each scandirection, an arrangement of context indexes may be adaptively changedfor each scan direction in the same manner as in the pattern 0. Forexample, context indexes are derived by using a pseudo-code illustratedin FIG. 73. Furthermore, the patterns 0 and 3 are the same as thepatterns 0 and 3 of the pseudo-code illustrated in FIG. 70, and thusdescription thereof will be omitted.

(Case of Pattern 1)

In a case of the up-right diagonal scan, the context indexes illustratedin FIG. 29(b) are derived from the following Equation.

sigCtx=(yB==0) ? 2:(yB==1) ? 1:0

In a case of the horizontal fast scan, the context indexes illustratedin FIG. 72(a) are derived from the following Equation.

sigCtx=(xB+3*yB<4) ? 2:(xB+3*yB<8) ? 1:0

In a case of the horizontal fast scan, the context indexes illustratedin FIG. 72(b) are derived from the following Equation.

sigCtx=(3*xB+yB<4) ? 2:(3*xB+yB<8) ? 1:0

(Case of Pattern 2)

In a case of the up-right diagonal scan, the context indexes illustratedin FIG. 29(c) are derived from the following Equation.

sigCtx=(xB==0) ? 2:(xB==1) ? 1:0

In a case of the horizontal fast scan, the context indexes illustratedin FIG. 72(a) are derived from the following Equation.

sigCtx=(xB+3*yB<4) ? 2:(xB+3*yB<8) ? 1:0

In a case of the horizontal fast scan, the context indexes illustratedin FIG. 72(b) are derived from the following Equation.

sigCtx=(3*xB+yB<4) ? 2:(3*xB+yB<8) ? 1:0

As mentioned above, according to the configuration of ModificationExample 8-2, in the moving image decoding apparatus 1, the context indexderiving means determines a sub-block coefficient presence/absence flagfor a right adjacent sub-block which is a sub-block adjacent to theright side of a process target sub-block and a lower adjacent sub-blockwhich is adjacent to the lower side thereof, and derives a context indexon the basis of the determination result.

When a scan index indicates up-right diagonal scan, the context indexderiving means derives the context index corresponding to a case wherean occurrence probability of a non-zero transform coefficient is high ina case where a sum of xB and yB indicating a coefficient position in asub-block is smaller than a first threshold value; derives the contextindex corresponding to a case where an occurrence probability of anon-zero transform coefficient is intermediate in a case where the sumof xB and yB is equal to or greater than the first threshold value andis smaller than a second threshold value; and derives the context indexcorresponding to a case where an occurrence probability of a non-zerotransform coefficient is low in a case where the sum of xB and yB isequal to or greater than the second threshold value.

In addition, when a scan index indicates horizontal fast scan, thecontext index deriving means derives the context index corresponding toa case where an occurrence probability of a non-zero transformcoefficient is high in a case where a value of a weight sum ofW1×xB+W2×yB defined from xB and yB indicating a coefficient position ina sub-block is smaller than a third threshold value; derives the contextindex corresponding to a case where an occurrence probability of anon-zero transform coefficient is intermediate in a case where a valueof the weight sum of W1×xB+W2×yB is equal to or greater than the thirdthreshold value and is smaller than a fourth threshold value; andderives the context index corresponding to a case where an occurrenceprobability of a non-zero transform coefficient is low in a case where avalue of the weight sum of W1×xB+W2×yB is equal to or greater than thefourth threshold value.

Further, when a scan index indicates the vertical fast scan, the contextindex deriving means derives the context index corresponding to a casewhere an occurrence probability of a non-zero transform coefficient ishigh in a case where a value of a weight sum of W3×xB+W4×yB defined fromxB and yB indicating a coefficient position in a sub-block is smallerthan a third threshold value; derives the context index corresponding toa case where an occurrence probability of a non-zero transformcoefficient is intermediate in a case where a value of the weight sum ofW3×xB+W4×yB is equal to or greater than the third threshold value and issmaller than a fourth threshold value; and derives the context indexcorresponding to a case where an occurrence probability of a non-zerotransform coefficient is low in a case where a value of the weight sumof W3×xB+W4×yB is equal to or greater than the fourth threshold value.

Therefore, since a context derivation pattern is changed in accordancewith a scan index, it is possible to realize a context derivationpattern which is more suitable for an actual occurrence probability oftransform coefficient for each scan direction indicated by the scanindex, and thus to improve coding efficiency. Particularly, in a casewhere derivation of a context index is made in common to TUs includingan 8×8 TU to a 32×32 TU, it is possible to derive a preferable contextindex which is more suitable for an actual occurrence probability of anon-zero transform coefficient by setting the first threshold value to 2and the second threshold value to 3 in relation to the up-right diagonalscan when the corresponding determination result indicates that anon-zero transform coefficient is not present in either the rightadjacent sub-block or the lower adjacent sub-block. In addition, thefirst threshold value may be set to 1, and the second threshold valuemay be set to 2. Further, in a case of the horizontal fast scan, bysetting the weighting factor W1 to 1, the weighting factor W2 to 2, thethird threshold value TH3 to 3, and the fourth threshold value TH4 to 5,it is possible to derive a preferable context index which is moresuitable for an actual occurrence probability of a non-zero transformcoefficient. Furthermore, in a case of the vertical fast scan, bysetting the weighting factor W2 to 2, the weighting factor W2 to 1, thethird threshold value TH3 to 3, and the fourth threshold value TH4 to 5,it is possible to derive a preferable context index which is moresuitable for an actual occurrence probability of a non-zero transformcoefficient.

In addition, it is possible to derive a preferable context index whichis more suitable for an actual occurrence probability of a non-zerotransform coefficient by setting the first threshold value to 1 and thesecond threshold value to 2 in relation to the up-right diagonal scanwhen the corresponding determination result indicates that a non-zerotransform coefficient is not present in one of the right adjacentsub-block and the lower adjacent sub-block. Further, in a case of thehorizontal fast scan, by setting the weighting factor W1 to 1, theweighting factor W2 to 3, the third threshold value TH3 to 4, and thefourth threshold value TH4 to 8, it is possible to derive a preferablecontext index which is more suitable for an actual occurrenceprobability of a non-zero transform coefficient. Furthermore, in a caseof the vertical fast scan, by setting the weighting factor W2 to 3, theweighting factor W2 to 1, the third threshold value TH3 to 4, and thefourth threshold value TH4 to 8, it is possible to derive a preferablecontext index which is more suitable for an actual occurrenceprobability of a non-zero transform coefficient.

In addition, in a case where the corresponding determination resultindicates that a non-zero transform coefficient is present in both ofthe right adjacent sub-block and the lower adjacent sub-block, a fixedcontext index is derived, and thus it is possible to simplify derivationof a context index.

Here, the weighting factors W1 to W4 used in W1×xB+W2×yB and W3×xB+W4×yBwhich are weighted sums of xB and yB are not limited the above-describedones, and may be arbitrarily set according to a directivity of a scantype. In addition, the threshold values TH1 to TH6 are not limited tothe above-described ones, and may be set according to an occurrencefrequency of a non-zero transform coefficient as appropriate.

In addition, in Modification Examples 8 to 8-2, an example in which theadjacent sub-block coefficient presence/absence context deriving unit124 c derives a context index of a non-zero transform coefficient for a8×8 TU to a 32×32 TU has been described, but may be applied to a 4×4 TU.In a case of the 4×4 TU, there is no adjacent sub-block having asub-block coefficient presence/absence flag which can be referred to,and thus a pattern index idxCG is only 0. In this case, since contextindex derivation of a non-zero transform coefficient for a 4×4 TU to a32×32 TU can be unified by the adjacent sub-block coefficientpresence/absence context deriving unit 124 c except for DC, it ispossible to achieve effects of reducing a circuit scale, simplifying acontext index deriving process, and reducing the number of contexts. Inaddition, also in relation to a DC component from a 4×4 TU to a 32×32TU, a context index may be derived by the adjacent sub-block coefficientpresence/absence context deriving unit 124 c. Consequently, it ispossible to achieve greater effects of reducing a circuit scale,simplifying a context index deriving process, and reducing the number ofcontexts.

(Flow of Process by Transform Coefficient Decoding Unit 120)

Hereinafter, with reference to FIGS. 39 to 42, a description will bemade of a flow of a process performed by the transform coefficientdecoding unit 120.

FIG. 39 is a flowchart illustrating a flow of a transform coefficientdecoding process performed by the transform coefficient decoding unit120.

(Step S21)

First, the coefficient decoding control unit 123 included in thetransform coefficient decoding unit 120 sets a scan index scanIdx.

(Step S22)

Next, the last coefficient position decoding unit 121 included in thetransform coefficient decoding unit 120 decodes the syntaxeslast_significant_coeff_x and last_significant_coeff_y indicating aposition of the last transform coefficient according to a scan order.

(Step S23)

Next, the coefficient decoding control unit 123 starts a loop in theunits of sub-blocks. In addition, with a sub-block having the lastcoefficient as a starting position of the loop, a decoding process isperformed in the sub-block units in a backward scan order of thesub-block scan.

(Step S24)

Next, the sub-block coefficient presence/absence flag decoding unit 127included in the transform coefficient decoding unit 120 decodes thesub-block coefficient presence/absence flagsignificant_coeff_group_flag.

(Step S25)

Next, the coefficient presence/absence flag coding unit 124 included inthe transform coefficient decoding unit 120 decodes each non-zerotransform coefficient presence/absence flag significant_coeff_flag in atarget sub-block.

(Step S26)

Next, the coefficient value decoding unit 125 included in the transformcoefficient decoding unit 120 decodes a sign and a size of a non-zerotransform coefficient in a target small group. This is performed by therespective syntaxes coeff_abs_level_greater1_flag,coeff_abs_level_greater2_flag, coeff_sign_flag, andcoeff_abs_level_remaining.

(Step S27)

This step is a terminal end of the loop having the sub-block as the unit(a terminal end of the loop having the sub-block of step S23 as theunit).

[Decoding Process of Sub-Block Coefficient Presence/Absence Flag]

FIG. 40 is a flowchart more specifically illustrating the process (stepS24 of FIG. 39) of decoding the sub-block coefficient presence/absenceflag.

The sub-block coefficient presence/absence flag decoding unit 127initializes a value of the sub-block coefficient presence/absence flagsignificant_coeff_group_flag included in a target frequency domainbefore starting a loop of the sub-block. This initialization process isperformed by setting a sub-block coefficient presence/absence flag of asub-block including a DC coefficient and a sub-block coefficientpresence/absence flag of a sub-block including the last coefficient to1, and by setting other sub-block coefficient presence/absence flags to0.

(Step S244)

The sub-block coefficient presence/absence flag coding unit 124 acquiresa position of the sub-block.

(Step S247)

The coefficient presence/absence flag coding unit 124 determines whetheror not the target sub-block is a sub-block including the lastcoefficient or a DC coefficient.

(Step S248)

In a case where the target sub-block is not a sub-block including thelast coefficient or the DC coefficient (No in step S247), thecoefficient presence/absence flag coding unit 124 decodes the sub-blockcoefficient presence/absence flag significant_coeff_group_flag.

[Decoding Process on Coefficient Presence/Absence Flag]

FIG. 41 is a flowchart more specifically illustrating the process (stepS25 of FIG. 39) of decoding each non-zero transform coefficientpresence/absence flag significant_coeff_flag in the sub-block.

(Step S254)

Next, the coefficient presence/absence flag coding unit 124 starts aloop in the target sub-block. The loop is a loop having a frequencycomponent as the unit.

(Step S255)

Next, the coefficient presence/absence flag coding unit 124 acquires aposition of a transform coefficient.

(Step S256)

Next, the coefficient presence/absence flag coding unit 124 determineswhether or not a non-zero transform coefficient is present in the targetsub-block.

(Step S257)

In a case where a non-zero transform coefficient is present in thetarget sub-block (Yes in step S256), the coefficient presence/absenceflag coding unit 124 determines whether or not the position of thetransform coefficient is the last position.

(Step S253)

In a case where the position of the transform coefficient is not thelast position (No in step S257), the coefficient presence/absence flagcoding unit 124 derives a context index with respect to the processtarget transform coefficient in a predetermined method. Details of theoperation will be described later.

(Step S258)

After step S253, the coefficient presence/absence flag coding unit 124decodes the transform coefficient presence/absence flagsignificant_coeff_flag.

(Step S259)

This step is a terminal end of the loop having the frequency componentin the target sub-block as the unit (a terminal end of the loop in thesub-block of step S259).

<<Context Index Deriving Process>>

FIG. 42 is a flowchart illustrating an example of a flow of the contextindex deriving process in the coefficient presence/absence flag codingunit 124. In other words, FIG. 42 is a flowchart illustrating operations(details of the operation of step S253 of FIG. 41) of the TU sizedetermining unit 124 a, the position context deriving unit 124 b, andthe adjacent sub-block coefficient presence/absence context derivingunit 124 c included in the coefficient presence/absence flag coding unit124.

(Step SB101)

The TU size determining unit 124 a determines whether or not a TU sizeis smaller than a predetermined size. For example, the followingExpression is used for the determination.

log 2TrafoWidth+log 2TrafoHeight<THSize

In addition, for example, 6 is used as the threshold value THSize. In acase where 6 is used as the threshold value THsize, it is determinedthat a 4×4 TU is smaller than the predetermined size. It is determinedthat an 8×8 TU, a 16×4 TU, a 4×16 TU, a 16×16 TU, a 32×4 TU, a 4×32 TU,and a 32×32 TU are equal to or larger than the predetermined size.Further, the threshold value THSize may be 0. In this case, it isdetermined that the 4×4 TU to the 32×32 TU are equal to or larger thanthe predetermined size.

(Step SB104)

In a case where the process target TU size is equal to or larger thanthe predetermined size (No in step SB101), the TU size determining unit124 a selects the adjacent sub-block coefficient presence/absencecontext deriving unit 124 c as context deriving means, and a contextindex of the target transform coefficient is derived by the selectedadjacent sub-block coefficient presence/absence context deriving unit124 c.

(Step SB105)

In a case where the process target TU size is smaller than thepredetermined size (Yes in step SB101), the TU size determining unit 124a selects the position context deriving unit 124 b as context derivingmeans, and a context index of the target transform coefficient isderived by the selected position context deriving unit 124 b.

In addition, the TU size determining unit 124 a is not limited thereto,and may perform a process of deriving a context index ctxIdx which iscommon to TU sizes from the 4×4 TU to the 32×32 TU. In other words, theTU size determining unit 124 a may fixedly select either the positioncontext deriving unit 124 b or the adjacent sub-block coefficientpresence/absence context deriving unit 124 c regardless of a TU size.

[Moving Image Coding Apparatus 2]

With reference to FIGS. 43 to 47, a description will be made of aconfiguration of the moving image coding apparatus 2 according to thepresent embodiment. The moving image coding apparatus 2 is a codingapparatus which employs the technique used in the H. 264/MPEG-4. AVCstandard, and the technique proposed in High-Efficiency Video Coding(HEVC) which is a succeeding codec thereof. In the following, the sameparts as described above are given the same reference numerals, anddescription thereof will be omitted.

FIG. 43 is a block diagram illustrating a configuration of the movingimage coding apparatus 2. As illustrated in FIG. 43, the moving imagecoding apparatus 2 includes a predicted image generating unit 21, atransform/quantization unit 22, an inverse quantization/inversetransform unit 23, an adder 24, a frame memory 25, a loop filter 26, avariable length code coding unit 27, and a subtractor 28. In addition,as illustrated in FIG. 43, the predicted image generating unit 21includes an intra-predicted image generating unit 21 a, a motion vectordetecting unit 21 b, an inter-predicted image generating unit 21 c, aprediction type control unit 21 d, and a motion vector redundancydeleting unit 21 e. The moving image coding apparatus 2 is an apparatuswhich codes a moving image #10 (coding target image) so as to generatethe coded data #1.

(Predicted Image Generating Unit 21)

The predicted image generating unit 21 recursively splits a processtarget LCU into one or a plurality of lower CUs, and further splits eachleaf CU into one or a plurality of partitions, so as to generate aninter-predicted image Pred_Inter using inter-frame prediction or anintra-predicted image Pred_Inra using intra-frame prediction. Thegenerated inter-predicted image Pred_Intra and intra-predicted imagePred_Intra are supplied to the adder 24 and the subtractor 28 aspredicted images Pred.

In addition, the predicted image generating unit 21 omits decoding ofother parameters belonging to a PU in relation to a PU to which a skipmode is applied. Further, (1) an aspect of split into lower CUs andpartitions in a target LCU, (2) whether or not a skip mode is applied,and (3) whether an inter-predicted image Pred_Intra or anintra-predicted image Pred_Intra is generated for each partition, aredetermined so as to optimize coding efficiency.

(Intra-Predicted Image Generating Unit 21 a)

The intra-predicted image generating unit 21 a generates a predictedimage Pred_Intra regarding each partition by using inter-frameprediction. Specifically, (1) a prediction mode used forintra-prediction in each partition is selected, and (2) a predictedimage Pred_Intra is generated from a decoded image P by using theselected prediction mode. The intra-predicted image generating unit 21 asupplies the generated intra-predicted image Pred_Intra to theprediction type control unit 21 d.

In addition, the intra-predicted image generating unit 21 a determinesan estimated prediction mode for a target partition from a predictionmode which is assigned to a peripheral partition of the targetpartition, and supplies an estimated prediction mode flag indicatingwhether or not the estimated prediction mode is the same as a predictionmode which is actually selected for the target partition, to thevariable length code coding unit 27 via the prediction type control unit21 d as part of an intra-prediction parameter PP_Intra. The variablelength code coding unit 27 includes the flag in the coded data #1.

Further, in a case where the estimated prediction mode for the targetpartition is different from the prediction mode which is actuallyselected for the target partition, the intra-predicted image generatingunit 21 a supplies a remaining prediction mode index indicating aprediction mode for the target partition, to the variable length codecoding unit 27 via the prediction type control unit 21 d as part of theintra-prediction parameter PP_Intra. The variable length code codingunit 27 includes the remaining prediction mode index in the coded data#1.

In addition, in a case where the predicted image Pred_Intra isgenerated, the intra-predicted image generating unit 21 a selects aprediction mode which causes coding efficiency to be further improved,from among the prediction modes illustrated in FIG. 11, and applies theselected prediction mode.

(Motion Vector Detecting Unit 21 b)

The motion vector detecting unit 21 b detects a motion vector mvregarding each partition. Specifically, (1) an adaptive filtered decodedimage P_ALF′ used as a reference image is selected, and (2) a regionwhich is most approximate to the target partition in the selectedadaptive filtered decoded image P_ALF′ is searched, so that the motionvector mv regarding the target partition is detected. Here, the adaptivefiltered decoded image P_ALF′ is an image obtained by the loop filter 26performing a filter process on a decoded image in which decoding of allframes have already been completed, and the motion vector detecting unit21 b may read a pixel value of each pixel forming the adaptive filtereddecoded image P_ALF′ from the frame memory 25. The motion vectordetecting unit 21 b supplies the detected motion vector mv to theinter-predicted image generating unit 21 c and the motion vectorredundancy deleting unit 21 e along with a reference image index RI fordesignating the adaptive filtered decoded image P_ALF′ used as areference image.

(Inter-Predicted Image Generating Unit 21 c)

The inter-predicted image generating unit 21 c generates a motioncompensation image me regarding each inter-prediction partition throughinter-frame prediction. Specifically, the motion compensation image meis generated from the adaptive filtered decoded image P_ALF′ designatedby the reference image index RI which is supplied from the motion vectordetecting unit 21 b, by using the motion vector mv supplied from themotion vector detecting unit 21 b. In the same manner as the motionvector detecting unit 21 b, the inter-predicted image generating unit 21c may read a pixel value of each pixel forming the adaptive filtereddecoded image P_ALF′ from the frame memory 25. The inter-predicted imagegenerating unit 21 c supplies the generated motion compensation image me(inter-predicted image Pred_Inter) to the prediction type control unit21 d along with the reference image index RI supplied from the motionvector detecting unit 21 b.

(Prediction Type Control Unit 21 d)

The prediction type control unit 21 d compares the intra-predicted imagePred_Intra and the inter-predicted image Pred_Inter with a coding targetimage, and selects whether intra-prediction or inter-prediction isperformed. In a case where the intra-prediction is selected, theprediction type control unit 21 d supplies the intra-predicted imagePred_Intra to the adder 24 and the subtractor 28 as a predicted imagePred, and also supplies the intra-prediction parameter PP_Intra which issupplied from the intra-predicted image generating unit 21 a, to thevariable length code coding unit 27. On the other hand, in a case wherethe inter-prediction is selected, the prediction type control unit 21 dsupplies the inter-predicted image Pred_Inter to the adder 24 and thesubtractor 28 as a predicted image Pred, and also supplies, to thevariable length code coding unit 27, the reference image index RI, andan estimated motion vector index PMVI and a motion vector residual MVDwhich are supplied from the motion vector redundancy deleting unit 21 edescribed later, as inter-prediction parameters PP_Inter. In addition,the prediction type control unit 21 d supplies prediction typeinformation Pred_type indicating which one of the intra-predicted imagePred_Intra and the inter-predicted image Pred_Inter has been selected,to the variable length code coding unit 27.

(Motion Vector Redundancy Deleting Unit 21 e)

The motion vector redundancy deleting unit 21 e deletes redundancy fromthe motion vector mv which has been detected by the motion vectordetecting unit 21 b. Specifically, (1) an estimation method used toestimate the motion vector mv is selected, (2) an estimated motionvector pmv is derived according to the selected estimation method, and(3) the motion vector residual MVD is generated by subtracting theestimated motion vector pmv from the motion vector mv. The motion vectorredundancy deleting unit 21 e supplies the generated motion vectorresidual MVD to the prediction type control unit 21 d along with theestimated motion vector index PMVI indicating the selected estimationmethod.

(Transform/Quantization Unit 22)

The transform/quantization unit 22 (1) performs frequency transform suchas discrete cosine transform (DCT) on a prediction residual D obtainedby subtracting the predicted image Pred from the coding target image,for each block (transform unit), (2) quantizes a transform coefficientCoeff_IQ which is obtained through the frequency transform, and (3)supplies the transform coefficient Coeff obtained through thequantization to the variable length code coding unit 27 and the inversequantization/inverse transform unit 23. In addition, thetransform/quantization unit 22 (1) selects a quantization step QP usedfor the quantization for each TU, (2) supplies a quantization parameterdifference Δpq indicating a size of the selected quantization step QP tothe variable length code coding unit 27, and (3) supplies the selectedquantization step QP to the inverse quantization/inverse transform unit23. Here, the quantization parameter difference Δpq indicates adifference value obtained by subtracting a value of a quantizationparameter qp′ regarding a TU which has previously undergone frequencytransform and quantization from a quantization parameter qp (forexample, QP=2^(pq/6)) regarding a TU which undergoes frequency transformand quantization.

In addition, the DCT performed by the transform/quantization unit 22 isgiven by, for example, the following Equation (2) in a case where a sizeof a target block is 8×8 pixels, and an unquantized transformcoefficient for a horizontal frequency u and a vertical frequency v isdenoted by Coeff_IQ(u,v) (where 0≤u≤7 and 0≤v≤7).

$\begin{matrix}{\mspace{79mu} \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack} & \; \\{{{Coeff\_ IQ}\left( {u,v} \right)} = {\frac{1}{4}C(u){C(v)}{\sum\limits_{i = 0}^{7}{\sum\limits_{j = 0}^{7}{{D\left( {i,j} \right)}\cos \left\{ \frac{\left( {{2i} + 1} \right)u\; \pi}{16} \right\} \cos \left\{ \frac{\left( {{2j} + 1} \right)v\; \pi}{16} \right\}}}}}} & (2)\end{matrix}$

Here, D(i,j) (where 0≤u≤7 and 0≤v≤7) indicates a prediction residual Dat a position (i,j) in a target block. In addition, C(u) and C(v) aregiven as follows.

C(u)=1/√2 (u=0)

C(u)=1 (u≠0)

C(v)=1/√2 (v=0)

C(v)=1 (v≠0)

(Inverse Quantization/Inverse Transform Unit 23)

The inverse quantization/inverse transform unit 23 (1) inverselyquantizes the quantized transform coefficient Coeff, (2) performsinverse frequency transform such as inverse discrete cosine transform(DCT) on the transform coefficient Coeff_IQ obtained through the inversequantization, and (3) supplies the prediction residual D to the adder24. The quantization step QP which is supplied from thetransform/quantization unit 22 is used to inversely quantize thequantized transform coefficient Coeff. In addition, the predictionresidual D which is output from the inverse quantization/inversetransform unit 23 is obtained by adding an quantization error to theprediction residual D which is input to the transform/quantization unit22, but, here, for simplification, the common name is used. Morespecific operations of the inverse quantization/inverse transform unit23 is substantially the same as the inverse quantization/inversetransform unit 13 included in the moving image decoding apparatus 1.

(Adder 24)

The adder 24 adds the predicted image Pred selected in the predictiontype control unit 21 d to the prediction residual D generated in theinverse quantization/inverse transform unit 23, so as to generate a(local) decoded image P. The generated (local) decoded image P generatedin the adder 24 is supplied to the loop filter 26 and is also stored inthe frame memory 25 so as to be used as a reference image inintra-prediction.

(Variable Length Code Coding Unit 27)

The variable length code coding unit 27 performs variable length codingon (1) the quantized transform coefficient Coeff and Δqp which aresupplied from the transform/quantization unit 22, (2) the quantizationparameters (the inter-predicted image Pred_Inter and the intra-predictedimage Pred_Intra) supplied from the prediction type control unit 21 d,(3) the prediction type information Pred_type, and (4) a filterparameter FP supplied from the loop filter 26, so as to generate thecoded data #1.

FIG. 44 is a block diagram illustrating a configuration of the variablelength code coding unit 27. As illustrated in FIG. 44, the variablelength code coding unit 27 includes a quantized residual informationcoding unit 271 which codes the quantized transform coefficient Coeff, aprediction parameter coding unit 272 which codes the predictionparameter PP, a prediction type information coding unit 273 which codesthe prediction type information Pred_type, and a filter parameter codingunit 274 which codes the filter parameter PP. A specific configurationof the quantized residual information coding unit 271 will be describedlater, and thus description thereof will be omitted here.

(Subtractor 28)

The subtractor 28 subtracts the predicted image Pred selected in theprediction type control unit 21 d from the coding target image so as togenerate the prediction residual D. The prediction residual D generatedin the subtractor 28 undergoes frequency transform and quantization inthe transform/quantization unit 22.

(Loop Filter 26)

The loop filter 26 functions (1) as a deblocking filter (DF) whichperforms smoothing (deblock process) on a peripheral image on a blockboundary or a partition boundary in the decoded image P, and (2) as anadaptive filter (ALF) of performing an adaptive filter process on theimage to which the deblocking filter has been applied, by using thefilter parameter FP.

(Details of Quantized Residual Information Coding Unit 271)

The quantized residual information coding unit 271 performscontext-based adaptive binary arithmetic coding on the quantizedtransform coefficient Coeff (xC,yC) so as to generate quantized residualinformation QD. Syntax included in the quantized residual information QDwhich is generated is as described above.

In addition, xC and yC are indexes indicating a position of eachfrequency component in a frequency domain, and are indexes correspondingto the above-described horizontal frequency u and vertical frequency v.Further, hereinafter, the quantized transform coefficient Coeff issimply referred to as a transform coefficient Coeff in some cases.

FIG. 45 is a block diagram illustrating a configuration of the quantizedresidual information coding unit 271. As illustrated in FIG. 45, thequantized residual information coding unit 271 includes a transformcoefficient coding unit 220 and an arithmetic code coding unit 230.

(Arithmetic Code Coding Unit 230)

The arithmetic code coding unit 230 codes each Bin supplied from thetransform coefficient coding unit 220 by referring to context, so as togenerate the quantized residual information QD, and includes a contextrecording/updating unit 231 and a bit coding unit 232 as illustrated inFIG. 45.

(Context Recording/Updating Unit 231)

The context recording/updating unit 231 has a configuration forrecording and updating a context variable CV which is managed by eachcontext index ctxIdx. Here, the context variable CV includes (1) asuperior symbol MPS (most probable symbol) of which an occurrenceprobability is high, and (2) a probability state index pStateIdx fordesignating an occurrence probability of the superior symbol MPS.

The context recording/updating unit 231 updates the context variable CVby referring to the context index ctxIdx supplied from each constituentelement included in the transform coefficient coding unit 220 and avalue of a Bin coded by the bit coding unit 232, and records the updatedcontext variable CV until the next update. In addition, the superiorsymbol MPS is 0 or 1. Further, the superior symbol MPS and theprobability state index pStateIdx are updated whenever the bit codingunit 232 decodes a single Bin.

In addition, the context index ctxIdx may directly designate context foreach frequency component, and may be an increment value from an offsetof a context index which is set for each process target TU (this is alsothe same for the following).

[Bit Coding Unit 232]

The bit coding unit 232 codes each Bin supplied from each constituentelement included in the transform coefficient coding unit 220 byreferring to the context variable CV which is recorded in the contextrecording/updating unit 231, so as to generate the quantized residualinformation QD. In addition, a value of the coded Bin is also suppliedto the context recording/updating unit 231 so as to be referred to forupdating the context variable CV.

(Transform Coefficient Coding Unit 220)

As illustrated in FIG. 45, the transform coefficient coding unit 220includes a last coefficient position coding unit 221, a scan order tablestorage unit 222, a coefficient coding control unit 223, a coefficientpresence/absence flag coding unit 224, a coefficient value coding unit225, a coded coefficient storage unit 226, a sub-block coefficientpresence/absence flag coding unit 227, and syntax deriving unit 228.

[Syntax Deriving Unit 228]

The syntax deriving unit 228 refers to each value of the transformcoefficient Coeff (xC,yC), and derives each value of syntaxeslast_significant_coeff_x, last_significant_coeff_y,significant_coeff_flag, coeff_abs_level_greater1_flag,coeff_abs_level_greater2_flag, coeff_sign_flag, andcoeff_abs_level_remaining, for specifying the transform coefficient in atarget frequency domain. The derived each syntax is supplied to thecoded coefficient storage unit 226. In addition, among the derivedsyntaxes, last_significant_coeff_x and last_significant_coeff_y are alsosupplied to the coefficient coding control unit 223 and the lastcoefficient position coding unit 221. Further, among the derivedsyntaxes, significant_coeff_flag is also supplied to the coefficientpresence/absence flag coding unit 224. Furthermore, the contentindicated by each syntax has been described above, and thus descriptionthereof will be omitted here.

[Last Coefficient Position Coding Unit 221]

The last coefficient position coding unit 221 generates Bins indicatingthe syntaxes last_significant_coeff_x and last_significant_coeff_ysupplied from the syntax deriving unit 228. In addition, the generatedeach Bin is supplied to the bit coding unit 232. Further, the contextindex ctxIdx for designating context which is referred to for coding theBin of the syntaxes last_significant_coeff_x andlast_significant_coeff_y is supplied to the context recording/updatingunit 231.

[Scan Order Table Storage Unit 222]

The scan order table storage unit 222 stores a table which provides aposition of a process target frequency component in a frequency domainby using a size of a process target TU (block), a scan index indicatingthe type of scan direction, and a frequency component identificationindex which is given according to a scan order, as arguments. An exampleof such a scan order table may include ScanOrder illustrated in FIGS. 4and 5.

In addition, the scan order table storage unit 222 stores a sub-blockscan order table for designating a scan order of sub-blocks. Here, thesub-block scan order table is designated by a size of a process targetTU (block) and the scan index scanIdx associated with a prediction modeindex of an intra-prediction mode.

The scan order table and sub-block scan order table stored in the scanorder table storage unit 222 are the same as those stored in the scanorder table storage unit 122 of the moving image decoding apparatus 1,and thus description thereof will be omitted here.

[Coefficient Coding Control Unit 223]

The coefficient coding control unit 223 has a configuration forcontrolling an order of a coding process in each constituent elementincluded in the quantized residual information coding unit 271.

Specifically, the coefficient coding control unit 223 performs sub-blocksplitting, the supply of each sub-block position according to asub-block scan order, and the supply of a position of each frequencycomponent in a sub-block according to a scan order.

The coefficient coding control unit 223 derives a sub-block size inaccordance with a scan order and/or a TU size, and splits the TU in thederived sub-block size so as to split the TU into sub-blocks. Asplitting method is as described in FIGS. 14 and 15, and thusdescription thereof will be omitted here.

(In Case where TU Size is Equal to or Smaller than Predetermined Size)

In a case where a TU size is equal to or smaller than a predeterminedsize (for example, a 4×4 TU or the like), the coefficient coding controlunit 223 specifies a position of the last non-zero transform coefficientaccording to a forward scan by referring to the syntaxeslast_significant_coeff_x and last_significant_coeff_y supplied from thesyntax deriving unit 228, and supplies a position (xC,yC) of eachfrequency component to the sub-block coefficient presence/absence flagcoding unit in a backward scan order of a scan order which uses thespecified position of the last non-zero transform coefficient as astarting point and is given by the sub-block scan order table stored inthe scan order table storage unit 222.

In addition, the coefficient coding control unit 223 supplies a size ofa process target TU to each constituent element (not illustrated)included in the transform coefficient coding unit 220.

Further, the coefficient coding control unit 223 may supply the position(xC,yC) of each frequency component to the coefficient presence/absenceflag coding unit 224 in a forward scan order of a scan order which isgiven by the scan order table stored in the scan order table storageunit 222.

(Case of TU Size is Larger than Predetermined Size)

In a case where a TU size is larger than a predetermined size, thecoefficient coding control unit 223 specifies a position of the lastnon-zero transform coefficient according to a forward scan by referringto the syntaxes last_significant_coeff_x and last_significant_coeff_ysupplied from the syntax deriving unit 228, and supplies a position(xCG,yCG) of each sub-block to the sub-block coefficientpresence/absence flag coding unit 227 in a backward scan order of a scanorder which uses a position of a sub-block including the specifiedposition of the last non-zero transform coefficient as a starting pointand is given by the sub-block scan order table stored in the scan ordertable storage unit 222.

Further, in relation to a process target sub-block, the coefficientcoding control unit 223 supplies a position (xC,yC) of each frequencycomponent included in the process target sub-block to the coefficientpresence/absence flag coding unit 224 in a backward scan order given bythe scan order table stored in the scan order table storage unit 222.Here, as a scan order of each frequency component included in theprocess target sub-block, in a case of intra-prediction, a scan order(any one of the horizontal fast scan, the vertical fast scan, and theup-right diagonal scan) indicated by a scan index scanIdx which isdesignated by the intra-prediction mode index IntraPredMode and a valuelog 2TrafoSize for designating a TU size may be used, and, in a case ofinter-prediction, the up-right diagonal scan may be used. Furthermore,the coefficient coding control unit 223 supplies a size of acorresponding TU and a scan index scanIdx associated with a predictionmode of the TU, to the coefficient presence/absence flag coding unit224.

As mentioned above, the coefficient coding control unit 223 changes ascan order for each intra-prediction mode. Generally, Generally, sincean intra-prediction mode and a bias of a transform coefficient arecorrelated with each other, a scan order is changed according to theintra-prediction mode, and a scan suitable for biases of the sub-blockcoefficient presence/absence flag and the coefficient presence/absenceflag can be performed. Consequently, it is possible to reduce a codeamount of the sub-block coefficient presence/absence flag and thecoefficient presence/absence flag which are coding and decoding targets,and thus to reduce a processing amount and to improve coding efficiency.

[Coefficient Value Coding Unit 225]

The coefficient value coding unit 225 generates Bins indicating thesyntaxes coeff_abs_level_greater1_flag, coeff_abs_level_greater2_flag,coeff_sign_flag, and coeff_abs_level_remaining, supplied from the syntaxderiving unit 228. In addition, each generated Bin is supplied to thebit coding unit 232. Further, the context index ctxIdx for designatingcontext which is referred to for coding the Bins of the syntaxes issupplied to the context recording/updating unit 231.

[Coefficient Presence/Absence Flag Coding Unit 224]

The coefficient presence/absence flag coding unit 224 according to thepresent embodiment codes syntax significant_coeff_flag[xC][yC]designated by each position (xC,yC). More specifically, a Bin indicatingthe syntax significant_coeff_flag[xC][yC] designated by each position(xC,yC) is generated. Each generated bit is supplied to the bit codingunit 232. In addition, the coefficient presence/absence flag coding unit224 calculates the context index ctxIdx for determining context which isused for the arithmetic code coding unit 230 to code the Bin of thesyntax significant_coeff_flag[xC][yC]. The calculated context indexctxIdx is supplied to the context recording/updating unit 231. Aspecific configuration example of the coefficient presence/absence flagcoding unit will be described later.

[Sub-Block Coefficient Presence/Absence Flag Coding Unit 227]

The sub-block coefficient presence/absence flag coding unit 227 codessyntax significant_coeff_group_flag[xCG][yCG] designated by eachsub-block position (xCG,yCG). More specifically, a Bin indicating syntaxsignificant_coeff_group_flag[xCG][yCG] designated by each sub-blockposition (xCG,yCG) is generated. Each generated Bin is supplied to thebit coding unit 232. In addition, the sub-block coefficientpresence/absence flag coding unit 227 calculates the context indexctxIdx for determining context which is used for the arithmetic codecoding unit 230 to code the Bin of the syntaxsignificant_coeff_flag[xC][yC]. The calculated context index ctxIdx issupplied to the context recording/updating unit 231.

FIG. 46 is a block diagram illustrating a configuration of the sub-blockcoefficient presence/absence flag coding unit 227. As illustrated inFIG. 46, the sub-block coefficient presence/absence flag coding unit 227includes a context deriving unit 227 a, a sub-block coefficientpresence/absence flag storage unit 227 b, and a sub-block coefficientpresence/absence flag setting unit 227 c.

Hereinafter, a description will be described by exemplifying a casewhere the sub-block position (xCG,yCG) is supplied from the coefficientcoding control unit 223 to the sub-block coefficient presence/absenceflag coding unit 227 in a forward scan order. In addition, in this case,the sub-block position (xCG, yCG) is preferably supplied to thesub-block coefficient presence/absence flag decoding unit 127 includedin the moving image decoding apparatus 1 in a backward scan order.

(Context Deriving Unit 227 a)

The context deriving unit 227 a included in the sub-block coefficientpresence/absence flag coding unit 227 derives a context index assignedto a sub-block which is designated by each sub-block position (xCG,yCG).The context index assigned to a sub-block is used to decode a Binindicating syntax significant_coeff_group_flag for the sub-block. Inaddition, in a case where the context index is derived, a value of thesub-block coefficient presence/absence flag stored in the sub-blockcoefficient presence/absence flag coding unit 227 is referred to. Thecontext deriving unit 227 a supplies the derived context index to thecontext recording/updating unit 231.

(Sub-Block Coefficient Presence/Absence Flag Storage Unit 227 b)

The sub-block coefficient presence/absence flag storage unit 227 bstores each value of the syntax significant_coeffgroup_flag suppliedfrom the coefficient presence/absence flag coding unit 224. Thesub-block coefficient presence/absence flag setting unit 227 c may readthe syntax significant_coeff_group_flag assigned to an adjacentsub-block from the sub-block coefficient presence/absence flag storageunit 227 b.

(Sub-Block Coefficient Presence/Absence Flag Setting Unit 227 c)

The sub-block coefficient presence/absence flag setting unit 227 cgenerates a Bin indicating the syntaxsignificant_coeff_group_flag[xCG][yCG] supplied from the coefficientpresence/absence flag coding unit 224. The generated Bin is supplied tothe bit coding unit 232.

<<Configuration Example of Coefficient Presence/Absence Flag Coding Unit224>>

FIG. 47 is a block diagram illustrating a configuration example of thecoefficient presence/absence flag coding unit 224 according to thepresent embodiment. The coefficient presence/absence flag coding unit224, as illustrated in FIG. 47, includes a TU size determining unit 224a, a position context deriving unit 224 b, an adjacent sub-blockcoefficient presence/absence context deriving unit 224 c, and acoefficient presence/absence flag setting unit 224 e.

(TU Size Determining Unit 224 a)

The TU size determining unit 224 a selects the position context derivingunit 224 b or the adjacent sub-block coefficient presence/absencecontext deriving unit 224 c according to a target TU size. Each selectedcontext deriving unit derives a context index ctxIdx.

For example, in a case where a TU size is equal to or smaller than apredetermined size (for example, in a case of a 4×4 TU), the TU sizedetermining unit 224 a selects the position context deriving unit 224 b.

Thus, the position context deriving unit 224 b derives a context indexctxIdx, and assigns the derived context index to a coding targetfrequency component.

On the other hand, in a case where the target TU size is larger than thepredetermined size (for example, in a case of an 8×8 TU, a 16×16 TU, a32×32 TU, or the like), the TU size determining unit 224 a selects theadjacent sub-block coefficient presence/absence context deriving unit224 c.

Thus, the adjacent sub-block coefficient presence/absence contextderiving unit 224 c derives a context index ctxIdx, and assigns thederived context index to a coding target frequency component.

In addition, the TU size determining unit 224 a is not limited to theabove-described configuration, and may have a configuration of derivinga context index ctxIdx which is common to TU sizes of a 4×4 TU to a32×32 TU. In other words, the TU size determining unit 224 a may have aconfiguration of fixedly selecting either one of the position contextderiving unit 224 b and the adjacent sub-block coefficientpresence/absence context deriving unit 224 c regardless of a TU size.

(Position Context Deriving Unit 224 b)

The position context deriving unit 224 b derives a context index ctxIdxfor a target frequency component on the basis of a position of thetarget frequency component in a frequency domain.

(Adjacent Sub-Block Coefficient Presence/Absence Context Deriving Unit224 c)

The adjacent sub-block coefficient presence/absence context derivingunit 224 c selects a context derivation pattern according to whether ornot a non-zero transform coefficient is present in an adjacentsub-block, and derives a context index for a coding target frequencycomponent from coordinates of the coding target frequency component in asub-block according to the selected derivation pattern.

(Coefficient Presence/Absence Flag Setting Unit 224 e)

The coefficient presence/absence flag setting unit 224 e generates a Binindicating the syntax significant_coeff_flag[xC][yC] supplied from thesyntax deriving unit 228. The generated is supplied to the bit codingunit 232. In addition, the coefficient presence/absence flag settingunit 224 e refers to a value of significant_coeff_flag[xC][yC] includedin a target sub-block, sets a value ofsignificant_coeff_group_flag[xCG][yCG] regarding the sub-block to 0 in acase where all values of significant_coeff_flag[xCG][yCG] are 0, thatis, a non-zero transform coefficient is not included in the targetsub-block, and, otherwise, sets a value ofsignificant_coeff_group_flag[xCG][yCG] regarding the target sub-blockto 1. significant_coeff_group_flag[xCG][yCG] given the values asmentioned above is supplied to the sub-block coefficientpresence/absence flag coding unit 227.

The above-described 224 has a configuration corresponding to that of thecoefficient presence/absence flag coding unit 124.

In other words, the TU size determining unit 224 a, the position contextderiving unit 224 b, the adjacent sub-block coefficient presence/absencecontext deriving unit 224 c, and the coefficient presence/absence flagsetting unit 224 e of the coefficient presence/absence flag coding unit224 respectively correspond to the TU size determining unit 124 a, theposition context deriving unit 124 b, the adjacent sub-block coefficientpresence/absence context deriving unit 124 c, and the coefficientpresence/absence flag setting unit 124 e of the coefficientpresence/absence flag coding unit 124.

For example, a specific process performed by the adjacent sub-blockcoefficient presence/absence context deriving unit 224 c is the same asthe process performed by the adjacent sub-block coefficientpresence/absence context deriving unit 124 c included in the movingimage decoding apparatus 1.

Therefore, details of each configuration of the coefficientpresence/absence flag coding unit 224 are the same as those described ineach configuration of the coefficient presence/absence flag coding unit124 described above. In other words, Examples and Modification Examples1 to 7 related to the moving image decoding apparatus 1, eachconfiguration of the moving image decoding apparatus 1 is replaced witha corresponding configuration of the coefficient presence/absence flagcoding unit 224, and thus the configuration of the coefficientpresence/absence flag coding unit 224 will be understood. Therefore,detailed description thereof will be omitted here.

As described above, the moving image coding apparatus 2 according to thepresent embodiment includes an arithmetic coding device whicharithmetically codes various elements of syntax indicating a transformcoefficient with respect to each transform coefficient which is obtainedfor each frequency component by performing frequency transform on atarget image for each unit domain. The arithmetic coding device includessub-block splitting means for splitting a target frequency domaincorresponding to a process target unit domain into sub-blocks eachhaving a predetermined size; sub-block coefficient presence/absence flagcoding means for coding a sub-block coefficient presence/absence flagindicating whether or not at least one non-zero transform coefficient isincluded in the sub-block with respect to the respective sub-blocks intowhich the frequency domain is split by the sub-block splitting means;non-zero transform coefficient determining means for determining whetheror not at least one non-zero transform coefficient is included in asub-block adjacent to a process target sub-block on the basis of thecoded sub-block coefficient presence/absence flag; and context indexderiving means for deriving a context index assigned to a transformcoefficient presence/absence flag which is syntax indicating whether ornot the transform coefficient is 0, in which, when a non-zero transformcoefficient is not present in any of sub-blocks adjacent to the processtarget sub-block, on the basis of the determination result, the contextindex deriving means derives the context indexes which respectivelycorrespond to a case where an occurrence probability of a non-zerotransform coefficient is low, a case where an occurrence probability ofa non-zero transform coefficient is high, and a case where an occurrenceprobability of a non-zero transform coefficient is intermediate betweenthe high case and the low case, according to a position of a processtarget transform coefficient in the process target sub-block.

In addition, as mentioned above, the moving image coding apparatus 2according to the present embodiment includes an arithmetic coding devicewhich arithmetically codes various elements of syntax indicating atransform coefficient with respect to each transform coefficient whichis obtained for each frequency component by performing frequencytransform on a target image for each unit domain. The arithmetic codingdevice includes sub-block splitting means for splitting a targetfrequency domain corresponding to a process target unit domain intosub-blocks each having a 4×4 size according to a predetermineddefinition; sub-block coefficient presence/absence flag coding means forcoding a sub-block coefficient presence/absence flag indicating whetheror not at least one non-zero transform coefficient is included in thesub-block with respect to the respective sub-blocks into which thefrequency domain is split by the sub-block splitting means; directivitydetermining means for determining a directivity of a distribution oftransform coefficients on the basis of a sub-block coefficientpresence/absence flag in a sub-block adjacent to a process targetsub-block; and context index deriving means for deriving a context indexassigned to a transform coefficient presence/absence flag which issyntax indicating whether or not the process target transformcoefficient is 0, in which, if coordinates of the sub-block having the4×4 size are set to (xB,yB) (where xB is a coordinate in a horizontaldirection, yB is a coordinate in a vertical direction, and the upperleft side of the sub-block is set to an origin (0,0)), when a scan orderapplied to the sub-block is up-right diagonal scan, in a case where adetermined directivity is a vertical direction, the context indexderiving means derives the context index corresponding to a case wherean occurrence probability of a transform coefficient is higher than indomains other than a domain formed by (0,0) to (0,3), (1,0) to (1,2),and (2,0), and in a case where a determined directivity is a horizontaldirection, the context index deriving means derives the context indexcorresponding to a case where an occurrence probability of a transformcoefficient is higher than in domains other than a domain formed by(0,0) to (3,0), (0,1) to (2,1), and (0,2).

In other words, the moving image coding apparatus 2 has a configurationcorresponding to the configuration of the above-described moving imagedecoding apparatus 1.

Therefore, according to the moving image coding apparatus 2, it ispossible to reduce a process amount related to coding and decoding of atransform coefficient in the same manner as in the moving image decodingapparatus 1.

In addition, the present invention may be represented as follows.According to an aspect of the present invention, there is a provided anarithmetic decoding device which decodes coded data which is obtained byarithmetically coding various elements of syntax indicating a transformcoefficient with respect to each transform coefficient which is obtainedfor each frequency component by performing frequency transform on atarget image for each unit domain, and includes sub-block splittingmeans for splitting a target frequency domain corresponding to a processtarget unit domain into sub-blocks each having a predetermined size;sub-block coefficient presence/absence flag decoding means for decodinga sub-block coefficient presence/absence flag indicating whether or notat least one non-zero transform coefficient is included in the sub-blockwith respect to the respective sub-blocks into which the frequencydomain is split by the sub-block splitting means; non-zero transformcoefficient determining means for determining whether or not at leastone non-zero transform coefficient is included in a sub-block adjacentto a process target sub-block on the basis of the decoded sub-blockcoefficient presence/absence flag; and context index deriving means forderiving a context index assigned to a transform coefficientpresence/absence flag which is syntax indicating whether or not thetransform coefficient is 0, in which, when a non-zero transformcoefficient is not present in any of sub-blocks adjacent to the processtarget sub-block, on the basis of the determination result, the contextindex deriving means derives the context indexes which respectivelycorrespond to a case where an occurrence probability of a non-zerotransform coefficient is low, a case where an occurrence probability ofa non-zero transform coefficient is high, and a case where an occurrenceprobability of a non-zero transform coefficient is intermediate betweenthe high case and the low case, according to a position of a processtarget transform coefficient in the process target sub-block.

There is a tendency for occurrence probabilities of a non-zero transformcoefficient in a process target sub-block to be different stepwisedepending on circumstances of values of sub-block coefficientpresence/absence flags of sub-blocks adjacent to the process targetsub-block.

For example, when there are present a right adjacent sub-block which isadjacent to the right side of a process target sub-block and a loweradjacent sub-block which is adjacent to the lower side thereof,distributions of the occurrence probability are different from eachother in a case where only a sub-block coefficient presence/absence flagin the right adjacent sub-block is 1 and in a case where only asub-block coefficient presence/absence flag in the lower adjacentsub-block is 1.

In addition, the distributions of the occurrence probability beingdifferent stepwise indicates that positions where an occurrenceprobability of a non-zero transform coefficient is high, approximatelyintermediate, and low are different in a process target sub-block.

According to the configuration, depending on circumstances of values ofsub-block coefficient presence/absence flags in sub-blocks adjacent to aprocess target sub-block, there is the derivation of context indexeswhich respectively correspond to a case where an occurrence probabilityof a non-zero transform coefficient is low, a case where an occurrenceprobability of a non-zero transform coefficient is high, and a casewhere an occurrence probability of a non-zero transform coefficient isapproximately intermediate between the high case and the low case.

Consequently, it is possible to realize a context derivation patternwhich is more suitable for an actual occurrence probability of atransform coefficient, and thus it is possible to improve codingefficiency.

In the arithmetic decoding device, preferably, the non-zero transformcoefficient determining means determines a sub-block coefficientpresence/absence flag for a right adjacent sub-block which is asub-block adjacent to the right side of a process target sub-block and alower adjacent sub-block which is adjacent to the lower side thereof;and, when it is determined that a non-zero transform coefficient is notpresent in one of the right adjacent sub-block and the lower adjacentsub-block, the context index deriving means derives the context indexcorresponding to a case where an occurrence probability of a non-zerotransform coefficient is high, at a left end or right end position ofthe sub-block in an adjacent direction of a sub-block in which it isdetermined that a non-zero transform coefficient is not present.

In a case where a non-zero transform coefficient is present in the rightadjacent sub-block, an occurrence probability of a non-zero transformcoefficient tends to increase at the upper end of the process targetsub-block. In addition, in a case where a non-zero transform coefficientis present in the lower adjacent sub-block, an occurrence probability ofa non-zero transform coefficient tends to increase at the left end ofthe process target sub-block.

According to the configuration, it is possible to derive the contextindex corresponding to a case where an occurrence probability of anon-zero transform coefficient is high, at a left end or right endposition of the sub-block in an adjacent direction of a sub-block inwhich it is determined that a non-zero transform coefficient is notpresent.

As a result, it is possible to derive a context index which is moresuitable for an occurrence probability of a non-zero transformcoefficient as described above.

In order to solve the above-described problems, an arithmetic decodingdevice according to the present invention decodes coded data obtained byarithmetically coding various elements of syntax indicating a transformcoefficient with respect to each transform coefficient which is obtainedfor each frequency component by performing frequency transform on atarget image for each unit domain. The arithmetic decoding deviceincludes sub-block splitting means for splitting a target frequencydomain corresponding to a process target unit domain into sub-blockseach having a 4×4 size according to a predetermined definition;sub-block coefficient presence/absence flag decoding means for decodinga sub-block coefficient presence/absence flag indicating whether or notat least one non-zero transform coefficient is included in the sub-blockwith respect to the respective sub-blocks into which the frequencydomain is split by the sub-block splitting means; directivitydetermining means for determining a directivity of a distribution oftransform coefficients on the basis of a sub-block coefficientpresence/absence flag in a sub-block adjacent to a process targetsub-block; and context index deriving means for deriving a context indexassigned to a transform coefficient presence/absence flag which issyntax indicating whether or not the process target transformcoefficient is 0, in which, if coordinates of the sub-block having the4×4 size are set to (xB,yB) (where xB is a coordinate in a horizontaldirection, yB is a coordinate in a vertical direction, and the upperleft side of the sub-block is set to an origin (0,0)), when a scan orderapplied to the sub-block is up-right diagonal scan, in a case where adetermined directivity is a vertical direction, the context indexderiving means derives the context index corresponding to a case wherean occurrence probability of a transform coefficient is higher than indomains other than a domain formed by (0,0) to (0,3), (1,0) to (1,2),and (2,0), and in a case where a determined directivity is a horizontaldirection, the context index deriving means derives the context indexcorresponding to a case where an occurrence probability of a transformcoefficient is higher than in domains other than a domain formed by(0,0) to (3,0), (0,1) to (2,1), and (0,2).

In the configuration, the directivity of a distribution of a transformcoefficient is, specifically, as follows in a case where there arepresent a right adjacent sub-block which is adjacent to the right sideof a process target sub-block and a lower adjacent sub-block which isadjacent to the lower side thereof.

In a case where a sub-block coefficient presence/absence flag in theright adjacent sub-block indicates that no non-zero transformcoefficient is included in the right adjacent sub-block, and a sub-blockcoefficient presence/absence flag in the lower adjacent sub-blockindicates that at least one non-zero transform coefficient is includedin the lower adjacent sub-block, an occurrence probability of a non-zerotransform coefficient tends to increase on the left side of the processtarget sub-block. In other words, in this case, the directivity of adistribution of a transform coefficient is a vertical direction.

In this case, an occurrence probability of a non-zero transformcoefficient is higher in a domain formed by (0,0) to (0,3), (1,0) to(1,2), and (2,0) than in domains other than the domain.

In addition, in a case where a sub-block coefficient presence/absenceflag in the right adjacent sub-block indicates that at least onenon-zero transform coefficient is included in the right adjacentsub-block, and a sub-block coefficient presence/absence flag in thelower adjacent sub-block indicates that no non-zero transformcoefficient is included in the lower adjacent sub-block, an occurrenceprobability of a non-zero transform coefficient tends to increase on theupper side of the process target sub-block. In other words, in thiscase, the directivity of a distribution of a transform coefficient is ahorizontal direction.

In this case, an occurrence probability of a non-zero transformcoefficient is higher in a domain formed by (0,0) to (3,0), (0,1) to(2,1), and (0,2) than in domains other than the domain.

Further, as a process order in a forward direction of up-right diagonalscan, in the coordinate expression, with (0,0) as a starting point, aprocess is applied from (0,1) to (1,0) in the upper right diagonaldirection, from (0,2) to (2,0) in the upper right diagonal direction,from (0,3) to (3,0) in the upper right diagonal direction, from (1,3) to(3,1) in the upper right diagonal direction, from (2,3) to (3,2) in theupper right diagonal direction, and finally to (3,3).

In addition, in the related art, a sequence of context indexes in abackward scan order (a scan order in an actual decoding process) of theup-right diagonal scan is as follows if a context index corresponding toa case where an occurrence probability of a transform coefficient ishigh is 1, and a context index corresponding to a case where anoccurrence probability of a transform coefficient is low is 0.

In case of horizontal direction: 0001001100110111

In case of vertical direction: 0000010011011111

As mentioned above, in a case of the horizontal direction, the number ofchanges from “0” to “1” is four, the number of changes from “1” to “0”is three, and thus the number of changes is a total of seven.

In addition, in a case of the vertical direction, the number of changesfrom “0” to “1” is three, the number of changes from “1” to “0” is two,and thus the number of changes is a total of five.

In contrast, according to the configuration, in a case where adetermined directivity is the vertical direction, there is thederivation of the context index corresponding to a case where anoccurrence probability of a transform coefficient is higher in a domainformed by (0,0) to (0,3), (1,0) to (1,2), and (2,0) than in domainsother than the domain.

In this case, a sequence of context indexes in a backward scan order ofthe up-right diagonal scan is as follows if a context indexcorresponding to a case where an occurrence probability of a transformcoefficient is high is 1, and a context index corresponding to a casewhere an occurrence probability of a transform coefficient is low is 0.

In case of vertical direction: 0000000011111111

Therefore, the number of changes in 0 and 1 is only one of a change from“0” to “1”.

In addition, in a case where a determined directivity is the horizontaldirection, there is the derivation of the context index corresponding toa case where an occurrence probability of a transform coefficient ishigher in a domain formed by (0,0) to (3,0), (0,1) to (2,1), and (0,2)than in domains other than the domain.

In this case, a sequence of context indexes in the backward scan orderis as follows in the same manner as above.

In case of horizontal direction: 0000001100111111

Therefore, the number of changes from “0” to “1” is two, the number ofchanges from “1” to “0” is one, and thus the number of changes is atotal of three.

As mentioned above, according to the configuration, it is possible tominimize changes in context indexes in a sub-block when compared withthe related art. Accordingly, as described above, in hardware whichdefines the number of repeated 0s and 1s, mounting of the hardware issimplified.

In order to solve the above-described problems, an arithmetic decodingdevice according to the present invention decodes coded data which isobtained by arithmetically coding various elements of syntax indicatinga transform coefficient with respect to each transform coefficient whichis obtained for each frequency component by performing frequencytransform on a target image for each unit domain. The arithmeticdecoding device includes sub-block splitting means for splitting atarget frequency domain corresponding to a process target unit domaininto sub-blocks each having a predetermined size; sub-block coefficientpresence/absence flag decoding means for decoding a sub-blockcoefficient presence/absence flag indicating whether or not at least onenon-zero transform coefficient is included in the sub-block with respectto the respective sub-blocks into which the frequency domain is split bythe sub-block splitting means; directivity determining means fordetermining a directivity of a distribution of transform coefficients onthe basis of a sub-block coefficient presence/absence flag in asub-block adjacent to a process target sub-block; and transformcoefficient decoding means for decoding the transform coefficients byusing a scan order according to a directivity determined by thedirectivity determining means.

According to the configuration, it is possible to decode a transformcoefficient by using a scan order according to a directivity of adistribution of a transform coefficient. Accordingly, it is possible tominimize changes in 0 and 1 in a backward scan order in a sub-block byusing a scan order according to a directivity even if the followingsequences of context indexes of the related.

In case of horizontal direction: 0001001100110111

In case of vertical direction: 0000010011011111

Accordingly, as described above, in hardware which defines the number ofrepeated 0s and 1s, mounting of the hardware is simplified.

In order to solve the above-described problems, an arithmetic decodingdevice according to the present invention decodes coded data which isobtained by arithmetically coding various elements of syntax indicatinga transform coefficient with respect to each transform coefficient whichis obtained for each frequency component by performing frequencytransform on a target image for each unit domain. The arithmeticdecoding device includes sub-block splitting means for splitting atarget frequency domain corresponding to a process target unit domaininto sub-blocks each having a predetermined size; sub-block coefficientpresence/absence flag decoding means for decoding a sub-blockcoefficient presence/absence flag indicating whether or not at least onenon-zero transform coefficient is included in the sub-block with respectto the respective sub-blocks into which the frequency domain is split bythe sub-block splitting means; coefficient-present-sub-block numbercounting means for counting the number of sub-blocks including at leastone non-zero transform coefficient for each sub-block adjacent to aprocess target sub-block on the basis of the sub-block coefficientpresence/absence flag; and context index deriving means for deriving acontext index assigned to a transform coefficient presence/absence flagwhich is syntax indicating whether or not the transform coefficient is0, in which the context index deriving means derives the context indexby using a sum of a coordinate in a horizontal direction and acoordinate in a vertical direction of a process target transformcoefficient in the process target sub-block according to the numbercounted by the coefficient-present-sub-block number counting means.

According to the configuration, it is possible to derive the contextindex by using a sum of a coordinate in a horizontal direction and acoordinate in a vertical direction of a process target transformcoefficient in the process target sub-block according to the number ofsub-blocks including at least one non-zero transform coefficient.

In the configuration, the sub-block coefficient presence/absence flag isnot differentiated between a right adjacent sub-block and a loweradjacent sub-block.

Accordingly, when compared with the above-described Example, it ispossible to reduce the number of context derivation patterns. Inaddition, the comparisons in the respective patterns are all performedthrough a comparison between “xB+yB” and a predetermined thresholdvalue. Further, the arrangements illustrated in FIGS. 24(a) to 24(c) arerelated to up-right diagonal scan, the number of changes in contextindexes in a scan order in a sub-block is only one, and thus mountingthereof in hardware is simplified.

As mentioned above, according to the configuration, it is possible toachieve an effect of simplifying mounting of hardware.

In order to solve the above-described problems, an arithmetic decodingdevice according to the present invention decodes coded data which isobtained by arithmetically coding various elements of syntax indicatinga transform coefficient with respect to each transform coefficient whichis obtained for each frequency component by performing frequencytransform on a target image for each unit domain. The arithmeticdecoding device includes sub-block splitting means for splitting atarget frequency domain corresponding to a process target unit domaininto sub-blocks each having a 4×4 size according to a predetermineddefinition; sub-block coefficient presence/absence flag decoding meansfor decoding a sub-block coefficient presence/absence flag indicatingwhether or not at least one non-zero transform coefficient is includedin the sub-block with respect to the respective sub-blocks into whichthe frequency domain is split by the sub-block splitting means; patterndetermining means for determining a pattern of a value of a sub-blockcoefficient presence/absence flag which is decoded for each sub-blockadjacent to a process target sub-block; and context index deriving meansfor deriving a context index assigned to a transform coefficientpresence/absence flag which is syntax indicating whether or not theprocess target transform coefficient is 0, in which the context indexderiving means derives the context index by using higher-order bits in2-bit expression of each of coordinates in a horizontal direction and avertical direction of a process target transform coefficient in theprocess target sub-block according to a determination result from thepattern determining means.

According to the configuration, it is possible to derive the contextindex by using higher-order bits in 2-bit expression of each ofcoordinates in a horizontal direction and a vertical direction of aprocess target transform coefficient in the process target sub-blockaccording to circumstances values of sub-block coefficientpresence/absence flags which are decoded for each sub-block adjacent toa process target sub-block

According to the configuration, it is possible to perform a contextindex deriving process from input information of 4 bits. Specifically,the 4 bits are a total of 4 bits including a higher bit (1 bit) of an Xcoordinate in a sub-block, a higher bit (1 bit) of a Y coordinate in thesub-block, a sub-block coefficient presence/absence flag (1 bit) in anadjacent sub-block in the X direction, and a sub-block coefficientpresence/absence flag (1 bit) in an adjacent sub-block in the Ydirection.

In addition, since derivation of output of 0 to 2 (2 bits) from input of4 bits is preferable, a context index deriving process can be performedthrough a simple bit calculation.

In order to solve the above-described problems, an arithmetic decodingdevice according to the present invention decodes coded data which isobtained by arithmetically coding various elements of syntax indicatinga transform coefficient with respect to each transform coefficient whichis obtained for each frequency component by performing frequencytransform on a target image for each unit domain. The arithmeticdecoding device includes sub-block splitting means for splitting atarget frequency domain corresponding to a process target unit domaininto sub-blocks each having a 4×4 size according to a predetermineddefinition; and transform coefficient decoding means for decoding atransform coefficient by using a scan order in a partial domain withrespect to respective partial domains each having a 2×2 size, obtainedby splitting the sub-block having the 4×4 size into four domains.

According to the configuration, a transform coefficient is decoded byusing a scan order in a partial domain with respect to respectivepartial domains each having a 2×2 size, obtained by splitting thesub-block having the 4×4 size into four domains.

As a scan order in the partial domain, upper left, upper right, lowerleft and lower right frequency components may be scanned in this order,for example, in a partial domain having a 2×2 size. In addition, a scanorder in the partial domain and a scan order of the partial domains(partial domain units) may be applied in a nested manner. Further, anactual decoding process may be performed a backward scan order.

According to the configuration, since coordinates in a scan order (forexample, coordinates of frequency components adjacent to each other inthe scan order) can be prevented from being considerably changed,transform coefficients which have spatially the same kinds ofcharacteristics as each other can be sequentially decoded. As a result,coding efficiency is improved.

In order to solve the above-described problems, an arithmetic decodingdevice according to the present invention decodes coded data which isobtained by arithmetically coding various elements of syntax indicatinga transform coefficient with respect to each transform coefficient whichis obtained for each frequency component by performing frequencytransform on a target image for each unit domain. The arithmeticdecoding device includes sub-block splitting means for splitting atarget frequency domain corresponding to a process target unit domaininto sub-blocks each having a predetermined size; sub-block coefficientpresence/absence flag decoding means for decoding a sub-blockcoefficient presence/absence flag indicating whether or not at least onenon-zero transform coefficient is included in the sub-block with respectto the respective sub-blocks into which the frequency domain is split bythe sub-block splitting means; directivity determining means fordetermining a directivity of a distribution of transform coefficients onthe basis of a sub-block coefficient presence/absence flag in asub-block adjacent to a process target sub-block; and context indexderiving means for deriving a context index assigned to a transformcoefficient presence/absence flag which is syntax indicating whether ornot the transform coefficient is 0, in which the context index derivingmeans derives the context index by using coordinates in the processtarget unit domain in the process target sub-block according to adirectivity determined by the directivity determining means.

According to the configuration, the context index is derived by usingcoordinates in the process target unit domain in the process targetsub-block according to a directivity of a distribution of a transformcoefficient.

In a case where a horizontal edge or a vertical edge is present,non-zero transform coefficients tend to concentrate and appear in adomain of xC=0 or yC=0 in a process target unit domain (for example, aTU).

According to the configuration, since a context index corresponding to acase where an occurrence probability of a non-zero transform coefficientis high is used in a case where a probability of the presence of thehorizontal edge or the vertical edge is high, it is possible to improvecoding efficiency.

In order to solve the above-described problems, an arithmetic decodingdevice according to the present invention decodes coded data which isobtained by arithmetically coding various elements of syntax indicatinga transform coefficient with respect to each transform coefficient whichis obtained for each frequency component by performing frequencytransform on a target image for each unit domain. The arithmeticdecoding device includes sub-block splitting means for splitting atarget frequency domain corresponding to a process target unit domaininto sub-blocks each having a predetermined size; sub-block coefficientpresence/absence flag decoding means for decoding a sub-blockcoefficient presence/absence flag indicating whether or not at least onenon-zero transform coefficient is included in the sub-block with respectto the respective sub-blocks into which the frequency domain is split bythe sub-block splitting means; adjacent sub-block coefficient presencedetermining means for determining whether or not at least one non-zerotransform coefficient is included in each of sub-blocks adjacent to aprocess target sub-block on the basis of the sub-block coefficientpresence/absence flag; and context index deriving means for deriving acontext index assigned to a transform coefficient presence/absence flagwhich is syntax indicating whether or not the transform coefficient is0, in which, in a case where at least one non-zero transform coefficientis included in sub-blocks of a predetermined number or more as a resultof the determination, the context index deriving means derives thecontext index corresponding to a case where an occurrence probability ofa non-zero transform coefficient is high, equally in the process targetsub-block.

According to the configuration, there is the derivation of the contextindex corresponding to a case where an occurrence probability of anon-zero transform coefficient is high, equally in the process targetsub-block.

As mentioned above, in a case where an occurrence probability of anon-zero transform coefficient is equally high, there is the derivationof the context index corresponding to a case where an occurrenceprobability of a non-zero transform coefficient is high, equally in theprocess target sub-block, and thus it is possible to improve codingefficiency.

An image decoding apparatus according to the present invention includesthe arithmetic decoding device; inverse frequency transform means forgenerating a residual image by performing inverse frequency transform ona transform coefficient which is decoded by the arithmetic decodingdevice; and decoded image generating means for generating a decodedimage by adding the residual image which is generated by the inversefrequency transform means to a predicted image which is predicted from agenerated decoded image.

The image decoding apparatus with this configuration also falls withinthe scope of the present invention, and also in this case, it ispossible to the same operations and effects as in the above-describedarithmetic decoding device.

In order to solve the above-described problems, an arithmetic codingdevice according to the present invention arithmetically codes variouselements of syntax indicating a transform coefficient with respect toeach transform coefficient which is obtained for each frequencycomponent by performing frequency transform on a target image for eachunit domain. The arithmetic coding device includes sub-block splittingmeans for splitting a target frequency domain corresponding to a processtarget unit domain into sub-blocks each having a predetermined size;sub-block coefficient presence/absence flag coding means for coding asub-block coefficient presence/absence flag indicating whether or not atleast one non-zero transform coefficient is included in the sub-blockwith respect to the respective sub-blocks into which the frequencydomain is split by the sub-block splitting means; non-zero transformcoefficient determining means for determining whether or not at leastone non-zero transform coefficient is included in a sub-block adjacentto a process target sub-block on the basis of the coded sub-blockcoefficient presence/absence flag; and context index deriving means forderiving a context index assigned to a transform coefficientpresence/absence flag which is syntax indicating whether or not thetransform coefficient is 0, in which, when a non-zero transformcoefficient is not present in any of sub-blocks adjacent to the processtarget sub-block, on the basis of the determination result, the contextindex deriving means derives the context indexes which respectivelycorrespond to a case where an occurrence probability of a non-zerotransform coefficient is low, a case where an occurrence probability ofa non-zero transform coefficient is high, and a case where an occurrenceprobability of a non-zero transform coefficient is intermediate betweenthe high case and the low case, according to a position of a processtarget transform coefficient in the process target sub-block.

In order to solve the above-described problem, an arithmetic codingdevice according to the present invention arithmetically codes variouselements of syntax indicating a transform coefficient with respect toeach transform coefficient which is obtained for each frequencycomponent by performing frequency transform on a target image for eachunit domain. The arithmetic coding device includes sub-block splittingmeans for splitting a target frequency domain corresponding to a processtarget unit domain into sub-blocks each having a 4×4 size according to apredetermined definition; sub-block coefficient presence/absence flagcoding means for coding a sub-block coefficient presence/absence flagindicating whether or not at least one non-zero transform coefficient isincluded in the sub-block with respect to the respective sub-blocks intowhich the frequency domain is split by the sub-block splitting means;directivity determining means for determining a directivity of adistribution of transform coefficients on the basis of a sub-blockcoefficient presence/absence flag in a sub-block adjacent to a processtarget sub-block; and context index deriving means for deriving acontext index assigned to a transform coefficient presence/absence flagwhich is syntax indicating whether or not the process target transformcoefficient is 0, in which, if coordinates of the sub-block having the4×4 size are set to (xB,yB) (where xB is a coordinate in a horizontaldirection, yB is a coordinate in a vertical direction, and the upperleft side of the sub-block is set to an origin (0,0)), when a scan orderapplied to the sub-block is up-right diagonal scan, in a case where adetermined directivity is a vertical direction, the context indexderiving means derives the context index corresponding to a case wherean occurrence probability of a transform coefficient is higher than indomains other than a domain formed by (0,0) to (0,3), (1,0) to (1,2),and (2,0), and in a case where a determined directivity is a horizontaldirection, the context index deriving means derives the context indexcorresponding to a case where an occurrence probability of a transformcoefficient is higher than in domains other than a domain formed by(0,0) to (3,0), (0,1) to (2,1), and (0,2).

In addition, an image coding apparatus according to the presentinvention includes transform coefficient generating means for generatinga transform coefficient by performing frequency transform on a residualimage between a coding target image and a predicted image for each unitdomain; and the arithmetic coding device, in which the arithmetic codingdevice generates coded data by arithmetically coding various elements ofsyntax indicating a transform coefficient which is generated by thetransform coefficient generating means.

The image coding apparatus with this configuration also falls within thescope of the present invention, and also in this case, it is possible tothe same operations and effects as in the above-described arithmeticcoding device.

APPENDIX 1

The above-described moving image coding apparatus 2 and moving imagedecoding apparatus 1 may be mounted and used in various elements ofequipment which perform transmission, reception, recording, andreproducing of moving images. In addition, the moving images may benatural images which are captured by a camera or the like, and may beartificial images (including CG and GUI) generated by a computer or thelike.

First, with reference to FIG. 48, a description will be made that theabove-described moving image coding apparatus 2 and moving imagedecoding apparatus 1 can be used for transmission and reception ofmoving images.

FIG. 48(a) is a block diagram illustrating a configuration oftransmission equipment including the moving image coding apparatus 2mounted therein. As illustrated in FIG. 48(a), transmission equipmentPROD_A includes a coder PROD_A1 which obtains by coding a moving image,a modulator PROD_A2 which obtains a modulated signal by modulating thecoded data obtained by the coder PROD_A1, and a transmitter PROD_A3which transmits the modulated signal obtained by the modulator PROD_A2.The above-described moving image coding apparatus 2 is used as the coderPROD_A1.

The transmission equipment PROD_A may further include a camera PROD_A4which captures a moving image as a supply source of a moving image whichis input to the coder PROD_A1, a recording medium PROD_A5 which recordsthe moving image thereon, an input terminal PROD_A6 for inputting amoving image from an external device, and an image processor PROD_A7which generates or processes an image. FIG. 48(a) illustrates aconfiguration in which the transmission equipment PROD_A includes allthe constituent elements, but some of the constituent elements may beomitted.

In addition, the recording medium PROD_A5 may record a moving imagewhich is not coded, and may record a moving image which is coded in acoding method for recording different from a coding method fortransmission. In the latter case, a decoder (not illustrated) whichdecodes coded data read from the recording medium PROD_A5 according to acoding method for recording may be provided between the recording mediumPROD_A5 and the coder PROD_A1.

FIG. 48(b) is a block diagram illustrating a configuration of receptionequipment including the moving image decoding apparatus 1 mountedtherein. As illustrated in FIG. 48(b), reception equipment PROD_Bincludes a receiver PROD_B1 which receives a modulated signal, ademodulator PROD_B2 which obtains coded data by demodulating themodulated signal received by the receiver PROD_B1, and a decoder PROD_B3which obtains a moving image by decoding the coded data obtained by thedemodulator PROD_B2. The above-described moving image decoding apparatus1 is used as the decoder PROD_B3.

The reception equipment PROD_B may further include a display PROD_B4which displays a moving image as a supply source of the moving imagewhich is output by the decoder PROD_B3, a recording medium PROD_B5 whichrecords a moving image, and an output terminal PROD_B6 which outputs amoving image to an external device. FIG. 48(b) illustrates aconfiguration in which the reception equipment PROD_B includes all theconstituent elements, but some of the constituent elements may beomitted.

In addition, the recording medium PROD_B5 may record a moving imagewhich is not coded, and may record a moving image which is coded in acoding method for recording different from a coding method fortransmission. In the latter case, a coder (not illustrated) which codesa moving image acquired from the decoder PROD_B3 according to a codingmethod for recording may be provided between the decoder PROD_B3 and therecording medium PROD_B5.

In addition, a transmission medium for transmitting a modulated signalmay be wireless and wired. Further, a transmission aspect oftransmitting a modulated signal may be broadcast (here, indicating atransmission aspect in which a transmission destination is not specifiedin advance) and may be communication (here, indicating a transmissionaspect in which a transmission destination is specified in advance). Inother words, transmission of a modulated signal may be realized by anyone of wireless broadcast, wired broadcast, wireless communication, andwired communication.

For example, a broadcasting station (a broadcasting facility or thelike) and a reception station (a television receiver or the like) interrestrial digital broadcasting are respectively examples of thetransmission equipment PROD_A and the reception equipment PROD_B whichtransmit and receive a modulated signal in wireless broadcast. Inaddition, a broadcasting station (a broadcasting facility or the like)and a reception station (a television receiver or the like) in cabletelevision broadcasting are respectively examples of the transmissionequipment PROD_A and the reception equipment PROD_B which transmit andreceive a modulated signal in wired broadcast.

In addition, a server (a workstation or the like) and a client (atelevision receiver, a personal computer, a smart phone, or the like) ina video on demand (VOD) service or a moving image sharing service usingthe Internet or the like are respectively examples of the transmissionequipment PROD_A and the reception equipment PROD_B which transmit andreceive a modulated signal in communication (typically, either awireless or wired medium is used as a transmission medium in a LAN, anda wired medium is used as a transmission medium in a WAN). Here, thepersonal computer includes a desktop PC, a laptop PC, and a tablet PC.Further, the smart phone also includes a multifunction mobile phoneterminal.

In addition, the client in the moving image sharing service has not onlya function of decoding coded data which is downloaded from the serverand displaying the data on a display but also a function of coding amoving image captured by a camera and uploading the moving image to theserver. In other words, the client in the moving image sharing servicefunctions as both of the transmission equipment PROD_A and the receptionequipment PROD_B.

Next, with reference to FIG. 49, a description will be made that theabove-described moving image coding apparatus 2 and moving imagedecoding apparatus 1 can be used for recording and reproducing movingimages.

FIG. 49(a) is a block diagram illustrating a configuration of recordingequipment PROD_C including the moving image coding apparatus 2 mountedtherein. As illustrated in FIG. 49(a), recording equipment PROD_Cincludes a coder PROD_C1 which obtains by coding a moving image, andwriter PROD_C2 which writes the coded data obtained by the coder PROD_C1on a recording medium PROD_M. The above-described moving image codingapparatus 2 is used as the coder PROD_C1.

In addition, the recording medium PROD_M may be (1) built into therecording equipment PROD_C, such as a hard disk drive (HDD), a solidstate drive (SSD), (2) connected to the recording equipment PROD_C, suchas a SD memory card or a universal serial bus (USB) flash memory, and(3) loaded in a drive device (not illustrated) built into the recordingequipment PROD_C, such as a digital versatile disc (DVD) or a Blu-rayDisc (registered trademark, BD).

In addition, the recording equipment PROD_C may further include a cameraPROD_C3 which captures a moving image as a supply source of a movingimage which is input to the coder PROD_C1, an input terminal PROD_C4 forinputting a moving image from an external device, a receiver PROD_C5which receives a moving image, and an image processor PROD_C6 whichgenerates or processes an image. FIG. 49(a) illustrates a configurationin which the recording equipment PROD_C includes all the constituentelements, but some of the constituent elements may be omitted.

Further, the receiver PROD_C5 may receive a moving image which is notcoded, and may receive a moving image which is coded in a coding methodfor recording different from a coding method for transmission. In thelatter case, a decoder (not illustrated) for transmission which decodescoded data which is coded in a coding method for transmission may beprovided between the receiver PROD_C5 and the coder PROD_C1.

The recording equipment PROD_C may include, for example, a DVD recorder,a BD recorder, and a hard disk drive (HDD) recorder (in this case, theinput terminal PROD_C4 or the receiver PROD_C5 is a main supply sourceof a moving image). Further, examples of the recording equipment PROD_Care also a camcorder (in this case, the camera PROD_C3 is a main supplysource of a moving image), a personal computer (in this case, thereceiver PROD_C5 or the image processor PROD_C6 is a main supply sourceof a moving image), and a smart phone (in this case, the camera PROD_C3or the receiver PROD_C5 is a main supply source of a moving image).

FIG. 49(b) is a block diagram illustrating a configuration ofreproducing equipment PROD_D including the moving image decodingapparatus 1 mounted therein. As illustrated in FIG. 49(b), reproducingequipment PROD_D includes a receiver PROD_1 includes a reader PROD_D1which reads coded data which is written on the recording medium PROD_M,and a coder PROD_D2 which obtains a moving image by coding the codeddata read by the reader PROD_D1. The above-described moving imagedecoding apparatus 1 is used as the decoder PROD_D2.

In addition, the recording medium PROD_M may be (1) built into thereproducing equipment PROD_D, such as an HDD, an SSD, (2) connected tothe reproducing equipment PROD_D, such as a SD memory card or a USBflash memory, and (3) loaded in a drive device (not illustrated) builtinto the reproducing equipment PROD_D, such as a DVD or a BD.

In addition, the reproducing equipment PROD_D may further include adisplay PROD_D3 which displays a moving image as a supply source of themoving image which is output by the decoder PROD_D2, an output terminalPROD_D4 which outputs a moving image to an external device, and atransmitter PROD_D5 which transmits a moving image. FIG. 49(b)illustrates a configuration in which the reproducing equipment PROD_Dincludes all the constituent elements, but some of the constituentelements may be omitted.

In addition, the transmitter PROD_D5 may transmit a moving image whichis not coded, and may transmit a moving image which is coded in a codingmethod for transmission different from a coding method for recording. Inthe latter case, a coder (not illustrated) which codes a moving image ina coding method for transmission may be provided between the decoderPROD_D2 and the transmitter PROD_D5.

The reproducing equipment PROD_D may include, for example, a DVD player,a BD player, and an HDD player (in this case, the output terminalPROD_D4 connected to a television receiver is a main supply source of amoving image). Further, examples of the reproducing equipment PROD_D arealso a television receiver (in this case, the display PROD_D3 is a mainsupply source of a moving image), a digital signage (also called anelectronic signboard or an electronic bulletin board; in this case, thedisplay PROD_D3 or the transmitter PROD_D5 is a main supply source of amoving image), a desktop PC (in this case, the output terminal PROD_D4or the transmitter PROD_D5 is a main supply source of a moving image), alaptop or tablet PC (in this case, the display PROD_D3 or thetransmitter PROD_D5 is a main supply source of a moving image), and asmart phone (in this case, the display PROD_D3 or the transmitterPROD_D5 is a main supply source of a moving image).

APPENDIX 2

Each block of the above-described moving image decoding apparatus 1 andmoving image coding apparatus 2 may be realized in hardware by usinglogic circuits formed on an integrated circuit (IC chip), and may berealized in software by using a central processing unit (CPU).

In the latter case, each of the apparatuses includes a CPU whichexecutes commands of a program, a read only memory (ROM) which storesthe program, a random access memory (RAM) on which the program isdeveloped, and a storage device (recording medium) such as a memorywhich stores the program and various items of data. In addition, theobject of the present invention can also be achieved by supplying arecording medium which causes a computer to read program codes (anexecutable program, an intermediate code program, or a source program)of a control program of each of the apparatuses which is software forrealizing the above-described functions, to each apparatus, and by thecomputer (or a CPU or an MPU) reading and executing the program codesrecorded on the recording medium.

As the recording medium, there may be the use of, for example, tapessuch as a magnetic tape or a cassette tape, disks or discs including amagnetic disk such as a floppy (registered trademark) or a hard disk andan optical disc such as a CD-ROM, an MO, an MD, a DVD, or a CD-R, cardssuch as an IC card (including a memory card) and an optical card,semiconductor memories such as a mask ROM, an EPROM, an EEPROM, and aflash ROM, or logic circuits such as a programmable logic device (PLD)and field programmable gate array (FPGA).

In addition, each of the apparatuses is configured to be connected to acommunication network, and the program codes may be supplied thereto viathe communication network. The communication network is not particularlylimited as long as the program codes can be transmitted. For example,the Internet, an intranet, an extranet, a LAN, an ISDN, a VAN, a CATV, acommunication network, a virtual private network, a telephone linenetwork, a mobile communication network, and a satellite communicationnetwork, may be used. In addition, a transmission medium forming thecommunication network is not particularly limited to a specificconfiguration or type as long as the program codes can be transmitted.The transmission medium may use a wired medium such as IEEE1394, a powerline carrier, a cable TV line, a telephone line, or an asymmetricdigital subscriber line (ADSL), and a wireless medium such as infraredrays in irDA or remote control, Bluetooth (registered trademark),IEEE802.11 wireless, High Data Rate (HDR), near field communication(NFC), Digital Living Network Alliance (DLNA), a mobile station network,a satellite line, or a terrestrial digital network.

The present invention is not limited to each of the above-describedembodiments and may have various modifications recited in the claims,and an embodiment obtained by appropriately combining the technicalmeans disclosed in the different embodiments is also included in thetechnical scope of the present invention.

INDUSTRIAL APPLICABILITY

The present invention can be suitably used for an arithmetic decodingdevice which decodes coded data which is arithmetically coded, and anarithmetic coding device which generates coded data which isarithmetically coded.

REFERENCE SIGNS LIST

-   -   1 MOVING IMAGE DECODING APPARATUS (IMAGE DECODING APPARATUS)    -   11 VARIABLE LENGTH CODE DECODING UNIT    -   111 QUANTIZED RESIDUAL INFORMATION DECODING UNIT (ARITHMETIC        DECODING DEVICE)    -   120 TRANSFORM COEFFICIENT DECODING UNIT (TRANSFORM COEFFICIENT        DECODING MEANS)    -   123 COEFFICIENT DECODING CONTROL UNIT (SUB-BLOCK SPLITTING        MEANS)    -   124 COEFFICIENT PRESENCE/ABSENCE FLAG DECODING UNIT    -   124 a TU SIZE DETERMINING UNIT    -   124 b POSITION CONTEXT DERIVING UNIT    -   124 c ADJACENT SUB-BLOCK COEFFICIENT PRESENCE/ABSENCE CONTEXT        DERIVING UNIT (CONTEXT INDEX DERIVING MEANS, NON-ZERO TRANSFORM        COEFFICIENT DETERMINING MEANS, PATTERN DETERMINING MEANS,        DIRECTIVITY DETERMINING MEANS)    -   124 e COEFFICIENT PRESENCE/ABSENCE FLAG SETTING UNIT    -   127 SUB-BLOCK COEFFICIENT PRESENCE/ABSENCE FLAG DECODING UNIT        (SUB-BLOCK COEFFICIENT PRESENCE/ABSENCE FLAG DECODING MEANS)    -   127 a CONTEXT DERIVING UNIT    -   127 b SUB-BLOCK COEFFICIENT PRESENCE/ABSENCE FLAG STORAGE UNIT    -   127 a SUB-BLOCK COEFFICIENT PRESENCE/ABSENCE FLAG SETTING UNIT    -   130 ARITHMETIC CODE DECODING UNIT    -   131 CONTEXT RECORDING/UPDATING UNIT    -   132 BIT DECODING UNIT    -   2 MOVING IMAGE CODING APPARATUS (IMAGE CODING APPARATUS)    -   27 VARIABLE LENGTH CODE CODING UNIT    -   271 QUANTIZED RESIDUAL INFORMATION CODING UNIT (ARITHMETIC        CODING DEVICE)    -   220 TRANSFORM COEFFICIENT CODING UNIT    -   223 COEFFICIENT CODING CONTROL UNIT (SUB-BLOCK SPLITTING MEANS)    -   224 COEFFICIENT PRESENCE/ABSENCE FLAG CODING UNIT    -   224 a TU SIZE DETERMINING UNIT    -   224 b POSITION CONTEXT DERIVING UNIT    -   224 c SUB-BLOCK COEFFICIENT PRESENCE/ABSENCE FLAG CONTEXT        DERIVING UNIT (CONTEXT INDEX DERIVING MEANS, NON-ZERO TRANSFORM        COEFFICIENT DETERMINING MEANS, DIRECTIVITY DETERMINING MEANS)    -   224 e COEFFICIENT PRESENCE/ABSENCE FLAG SETTING UNIT    -   227 SUB-BLOCK COEFFICIENT PRESENCE/ABSENCE FLAG CODING UNIT        (SUB-BLOCK COEFFICIENT PRESENCE/ABSENCE FLAG CODING MEANS)    -   227 a CONTEXT DERIVING UNIT    -   227 b SUB-BLOCK COEFFICIENT PRESENCE/ABSENCE FLAG STORAGE UNIT    -   227 c SUB-BLOCK COEFFICIENT PRESENCE/ABSENCE FLAG SETTING UNIT    -   228 SYNTAX DERIVING UNIT    -   230 ARITHMETIC CODE CODING UNIT    -   231 CONTEXT RECORDING/UPDATING UNIT    -   232 BIT CODING UNIT

1. A method for decoding coded data of a transform coefficient for eachunit domain, the method comprising: decoding a sub-block coefficientpresence/absence flag, for each of a plurality of sub-blocks, indicatingwhether or not one or more non-zero transform coefficient are includedin a respective one of the plurality of sub-blocks into which the unitdomain is split; and deriving a context index corresponding to atransform coefficient presence/absence flag indicating whether or not atransform coefficient of a target sub-block is 0, wherein when thenon-zero transform coefficient is not included in either the rightadjacent sub-block to the target sub-block or the lower adjacentsub-block to the target sub-block, deriving the context index having afirst value in a case where a sum of a horizontal coordinate and avertical coordinate indicating a position of the transform coefficientof the target sub-block is equal to a first threshold value, derivingthe context index having a second value in a case where the sum of thehorizontal coordinate and the vertical coordinate indicating theposition of the transform coefficient of the target sub-block is greaterthan the first threshold and is smaller than a second threshold value,and deriving the context index having a third value in a case where thesum of the horizontal coordinate and the vertical coordinate indicatingthe position of the transform coefficient of the target sub-block isequal to or greater than the second threshold, and when the non-zerotransform coefficient is included in both the right adjacent sub-blockto the target sub-block and the lower adjacent sub-block to the targetsub-block, deriving the context index having the first value regardlessof the position of the transform coefficient of the target sub-block. 2.The method of claim 1, wherein the unit domain is comprised by a frame,and further comprising displaying the frame on a display.
 3. An imagedecoding apparatus comprising a memory and a processor, wherein theprocessor configured to: decode a sub-block coefficient presence/absenceflag, for each of a plurality of sub-blocks, indicating whether or notone or more non-zero transform coefficient are included in a respectiveone of the plurality of sub-blocks into which the unit domain is split;and derive a context index corresponding to a transform coefficientpresence/absence flag indicating whether or not a transform coefficientof a target sub-block is 0, wherein when the non-zero transformcoefficient is not included in either the right adjacent sub-block tothe target sub-block or the lower adjacent sub-block to the targetsub-block, derive the context index having a first value in a case wherea sum of a horizontal coordinate and a vertical coordinate indicating aposition of the transform coefficient of the target sub-block is equalto a first threshold value, derive the context index having a secondvalue in a case where the sum of the horizontal coordinate and thevertical coordinate indicating the position of the transform coefficientof the target sub-block is greater than the first threshold and issmaller than a second threshold value, and derive the context indexhaving a third value in a case where the sum of the horizontalcoordinate and the vertical coordinate indicating the position of thetransform coefficient of the target sub-block is equal to or greaterthan the second threshold value, and when the non-zero transformcoefficient is included in both the right adjacent sub-block to thetarget sub-block and the lower adjacent sub-block to the targetsub-block, derive the context index having the first value regardless ofthe position of the transform coefficient of the target sub-block. 4.The image decoding apparatus of claim 3, wherein the unit domain iscomprised by a frame, and the processor is further configured to displaythe frame on a display.
 5. The image decoding apparatus of claim 4,wherein the image decoding apparatus comprises the display.
 6. The imagedecoding apparatus of claim 4, wherein the image decoding apparatus isone of a television, a desktop personal computer, a laptop personalcomputer, a phone, and a tablet.
 7. A method for arithmetically encodingeach element of syntax indicating a transform coefficient for each unitdomain, the method comprising: encoding a sub-block coefficientpresence/absence flag, for each of a plurality of sub-blocks, indicatingwhether or not one or more nonzero transform coefficient are included ina respective one of the plurality of sub-blocks into which the unitdomain is split; and deriving a context index corresponding to atransform coefficient presence/absence flag indicating whether or not atransform coefficient of a target sub-block is 0, wherein when thenon-zero transform coefficient is not included in either the rightadjacent sub-block to the target sub-block or the lower adjacentsub-block to the target sub-block, deriving the context index having afirst value in a case where a sum of a horizontal coordinate and avertical coordinate indicating a position of the transform coefficientof the target sub-block is equal to a first threshold value, derivingthe context index having a second value in a case where the sum of thehorizontal coordinate and the vertical coordinate indicating theposition of the transform coefficient of the target sub-block is greaterthan the first threshold and is smaller than a second threshold value,and deriving the context index having a third value in a case where thesum of the horizontal coordinate and the vertical coordinate indicatingthe position of the transform coefficient of the target sub-block isequal to or greater than the second threshold value, and when thenon-zero transform coefficient is included in both the right adjacentsub-block to the target sub-block and the lower adjacent sub-block tothe target sub-block, deriving the context index having the first valueregardless of the position of the transform coefficient of the targetsub-block.
 8. An image encoding apparatus comprising a memory and aprocessor, wherein the processor configured to: encode a sub-blockcoefficient presence/absence flag, for each of a plurality ofsub-blocks, indicating whether or not one or more non-zero transformcoefficient are included in a respective one of the plurality ofsub-blocks into which the unit domain is split; and derive a contextindex corresponding to a transform coefficient presence/absence flagindicating whether or not a transform coefficient of a target sub-blockis 0, wherein when the non-zero transform coefficient is not included ineither the right adjacent sub-block to the target sub-block or the loweradjacent sub-block to the target sub-block, derive the context indexhaving a first value in a case where a sum of a horizontal coordinateand a vertical coordinate indicating a position of the transformcoefficient of the target sub-block is equal to a first threshold value,derive the context index having a second value in a case where the sumof the horizontal coordinate and the vertical coordinate indicating theposition of the transform coefficient of the target sub-block is greaterthan the first threshold and is smaller than a second threshold value,and derive the context index having a third value in a case where thesum of the horizontal coordinate and the vertical coordinate indicatingthe position of the transform coefficient of the target sub-block isequal to or greater than the second threshold value, and when thenon-zero transform coefficient is included in both the right adjacentsub-block to the target sub-block and the lower adjacent sub-block tothe target sub-block, derive the context index having the first valueregardless of the position of the transform coefficient of the targetsub-block.